ci: update GitHub Actions runtimes

What:
- bump actions/checkout from v4 to v6 in CI and yolo workflows
- bump DeterminateSystems/nix-installer-action from v13 to v22

Why:
- remove Node 20 action runtime warnings before GitHub's Node 24 migration window
- keep the packaging pipelines on maintained action runtimes

Tests:
- ruby -e 'require "yaml"; YAML.load_file(".github/workflows/ci.yml"); YAML.load_file(".github/workflows/yolo-update.yml")'
- git diff --check

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
     timeout-minutes: 60
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Verify flake.lock owners
         run: scripts/check-flake-lock-owners.sh
@@ -38,10 +38,10 @@ jobs:
     timeout-minutes: 40
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v13
+        uses: DeterminateSystems/nix-installer-action@v22
 
       - name: Build Darwin CI aggregator
         timeout-minutes: 25

.github/workflows/yolo-update.yml

@@ -26,7 +26,7 @@ jobs:
       skipped_releases: ${{ steps.select.outputs.skipped_releases }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
@@ -67,7 +67,7 @@ jobs:
       materialization_digest: ${{ steps.materialization.outputs.materialization_digest }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Nix
         uses: cachix/install-nix-action@v31
@@ -116,10 +116,10 @@ jobs:
       materialization_digest: ${{ steps.materialization.outputs.materialization_digest }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v13
+        uses: DeterminateSystems/nix-installer-action@v22
 
       - name: Materialize selected release
         env:
@@ -164,12 +164,12 @@ jobs:
       contents: write
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
       - name: Install Nix
-        uses: DeterminateSystems/nix-installer-action@v13
+        uses: DeterminateSystems/nix-installer-action@v22
 
       - name: Promote selected release
         env: