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

Author: renovate-bot

.github/workflows/test.yml

@@ -7,7 +7,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: cachix/install-nix-action@v31
       with:
         github_access_token: ${{ secrets.GITHUB_TOKEN }}