Pin rust toolchain to 1.79.

This has been tested and works w/ the latest rust (1.81 as of this
commit). OKOS is now on NixOS 24.05:
oxidecomputer/offline-keystore-os#21.
NixOS 24.05 currently ships rust 1.79:
https://github.com/NixOS/nixpkgs/blob/fbca5e745367ae7632731639de5c21f29c8744ed/pkgs/development/compilers/rust/1_79.nix
We pin the rust toolchain version and update versions in CI to ensure
compatibility w/ the current OKOS version.

.github/workflows/formatting.yaml

@@ -10,5 +10,5 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           components: rustfmt
-          toolchain: 1.69.0
+          toolchain: 1.79
       - run: cargo fmt --check

.github/workflows/license-check.yaml

@@ -6,6 +6,6 @@ jobs:
     steps:
     - uses: actions/checkout@master
       with:
-        toolchain: 1.69.0
+        toolchain: 1.79
     - name: Check License Header
       uses: apache/skywalking-eyes/header@3ea9df11bb3a5a85665377d1fd10c02edecf2c40

.github/workflows/lint.yaml

@@ -10,7 +10,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           components: clippy
-          toolchain: 1.69.0
+          toolchain: 1.79
       - run: |
           sudo apt-get update
           sudo apt-get install -y pkg-config libudev-dev

.github/workflows/test.yaml

@@ -9,7 +9,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: 1.69.0
+          toolchain: 1.79
       - run: |
           sudo apt-get update
           sudo apt-get install -y pkg-config libudev-dev

rust-toolchain.toml

@@ -1,2 +1,2 @@
 [toolchain]
-channel = "1.69.0"
+channel = "1.79"