Bump actions/checkout from 3 to 4

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/test.yml

@@ -6,7 +6,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v22
     - run: nix-build -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz
     - run: nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz ./ci.nix --command 'true'