GHA: Update install-nix-action and checkout (#374)

`install-nix-action` was installing Nix 2.16 (!!!!!!!).

Let's uh. Get that updated.

Author: 9999years

.github/workflows/pages.yaml

@@ -15,15 +15,15 @@ jobs:
     name: Publish user manual to GitHub Pages
     runs-on: ubuntu-latest
     steps:
-      - uses: cachix/install-nix-action@6ed004b9ccb68dbc28e7c85bee15fa93dbd214ac # v22
+      - uses: cachix/install-nix-action@7be5dee1421f63d07e71ce6e0a9f8a4b07c2a487 # v31.6.1
         with:
           github_access_token: ${{ secrets.GITHUB_TOKEN }}
           extra_nix_config: |
             extra-experimental-features = nix-command flakes
             accept-flake-config = true
 
       - name: Checkout code
-        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
       - name: Build user manual
         run: |

.github/workflows/release.yaml

@@ -41,9 +41,9 @@ jobs:
       version: ${{ steps.get_cargo_metadata.outputs.version }}
     steps:
       - name: Checkout code
-        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
-      - uses: cachix/install-nix-action@6ed004b9ccb68dbc28e7c85bee15fa93dbd214ac # v22
+      - uses: cachix/install-nix-action@7be5dee1421f63d07e71ce6e0a9f8a4b07c2a487 # v31.6.1
         with:
           github_access_token: ${{ secrets.GITHUB_TOKEN }}
           extra_nix_config: |
@@ -68,7 +68,7 @@ jobs:
         os: [ubuntu-latest, macos-latest]
     steps:
       - name: Checkout code
-        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
       - name: Install rustup
         uses: dtolnay/rust-toolchain@4305c38b25d97ef35a8ad1f985ccf2d2242004f2 # stable
@@ -97,7 +97,7 @@ jobs:
             target/x86_64-apple-darwin/release/ghciwatch \
             target/aarch64-apple-darwin/release/ghciwatch
 
-      - uses: cachix/install-nix-action@6ed004b9ccb68dbc28e7c85bee15fa93dbd214ac # v22
+      - uses: cachix/install-nix-action@7be5dee1421f63d07e71ce6e0a9f8a4b07c2a487 # v31.6.1
         if: runner.os == 'Linux'
         with:
           github_access_token: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/version.yaml

@@ -63,12 +63,12 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
           # Fetch all history/tags (needed to compute versions)
           fetch-depth: 0
 
-      - uses: cachix/install-nix-action@6ed004b9ccb68dbc28e7c85bee15fa93dbd214ac # v22
+      - uses: cachix/install-nix-action@7be5dee1421f63d07e71ce6e0a9f8a4b07c2a487 # v31.6.1
         with:
           github_access_token: ${{ secrets.GITHUB_TOKEN }}
           extra_nix_config: |