add spack to PATH

[simonbyrne]

Thanks for putting this together. It would be helpful if the install spack action added spack to the current PATH. This can be done via the core.addPath function, or piping to the GITHUB_PATH variable

[vsoch]

@simonbyrne I replaced this with pakages https://github.com/syspack/pakages as a slightly better put together tool, but there is no reason you can't use the one here! As for the path, I'd be happy to accept a PR here to do that! core.AddPath is (I believe a typescript function?) and we are just using bash here, so it would use the latter.