chore(deps): update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     permissions:
       contents: read
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: cachix/install-nix-action@v31
@@ -31,7 +31,7 @@ jobs:
     needs:
       - tests
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - uses: cachix/install-nix-action@v31