Further attempts at building with .NET 8

[Numpsy]

Description

As #2818, but updated on top of the latest changes and with a couple of extra commits to try to get more tests passing - see further comments for details

[Numpsy]

Some of tests in previous runs seemed to be failing with dotnet/sdk#40655, whereby installing the dotnet tool in a subdirectory that contains a tools config file will ignore that file and use the one in the repo root, but then trying to use that tool will use the local config file and then fail.
That issue is marked as resolved, but it still seemed to be occuring in the SDK version used by the tests

[Numpsy]

I'm not sure what the logic for this (or cachedDotnetSdkReleases.json) should be when updating .NET versions.
The current cachedDotnetSdkReleases.json only contains the .NET 6 releases and that seemed to cause test failures when built as .NET 8 and looking for the v8 SDK versions.
Changing this to 8.0 fixed that, but that might then not be right if fake-cli is multi-targetted at .NET 6 and .NET 8 as the .NET 6 version might still need the list of v6 releases?

[github-actions]

Test Results

  3 files   -   6    3 suites   - 6   12m 9s ⏱️ - 35m 50s
441 tests  -   2  441 ✅  -   2  0 💤 ±0  0 ❌ ±0 
441 runs   - 822  441 ✅  - 822  0 💤 ±0  0 ❌ ±0 

Results for commit 0364d81. ± Comparison against base commit 78a2562.

This pull request removes 5 and adds 3 tests. Note that renamed tests count towards both.

[Fake.DotNet.FxCop.Tests; Test failure on non-Windows platforms]
[Fake.DotNet.ILMerge.Tests; Test failure on non-Windows platforms]
[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 6.0.300 SDK version assemblies and resolve runtime version from cached file]
[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 6.0.300 SDK version assemblies]
[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 6.0.301 SDK version assemblies]

[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 8.0.400 SDK version assemblies and resolve runtime version from cached file]
[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 8.0.400 SDK version assemblies]
[Fake.DotNet.sdkAssemblyResolverTests; Runner run script with 8.0.401 SDK version assemblies]

[Numpsy]

The remaining failures are in the TemplateIntegrationTests, with errors like

25h[11:48:10 ERR] Fake.DotNet.Cli.IntegrationTests.TemplateTests.can install and run the template.fails to build a target that doesn't exist failed in 00:00:09.6230000. 
Expected the message 'Target Nonexistent is not defined' but got: No exact match of product releases 8.0.401 found.
No product release found for 8.0.401. Maybe a pre-release? Returning all the versions.
No exact match of product releases 8.0.404 found.
No product release found for 8.0.404. Maybe a pre-release? Returning all the versions.
There was a problem while setting up the environment:
-> Could not find referenced assemblies in path: '[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.36\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.35\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.33\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.32\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.31\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.30\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.29\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.28\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.27\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.26\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.25\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.24\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.23\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.22\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.21\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.20\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.19\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.18\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.16\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.15\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.14\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.13\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.12\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.11\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.10\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.9\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.8\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.7\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.6\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.5\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.4\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.3\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.2\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.1\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-rc.2.21480.5\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-rc.1.21451.13\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.7.21377.19\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.6.21352.12\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.5.21301.5\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.4.21253.7\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.3.21201.4\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.2.21154.6\ref\net6.0],[C:\Users\runneradmin\AppData\Local\Microsoft\dotnet\packs\Microsoft.NETCore.App.Ref\6.0.0-preview.1.21102.12\ref\net6.0]', please check installed SDK and runtime versions

and I'm not sure if this is really a problem with the new stuff, or if it's because it's trying to use the 6.1.3 release to test the templates, and failing when running as .NET 8? (I suppose it shou;dn't be looking at the 6.0 assemblies when running as 8.0)