Bump actions/checkout from 3 to 4 in /.github/workflows

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

@@ -9,7 +9,7 @@ jobs:
   tests:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v20
       with:
         nix_path: nixpkgs=channel:nixos-unstable

.github/workflows/update-nixos-23.05.yaml

@@ -9,7 +9,7 @@ jobs:
     steps:
     - name: Get date
       run: echo "BRANCH_NAME=nixpkgs-update-$(date +'%Y-%m-%dT%H%M%S')" >> $GITHUB_ENV
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v20
       with:
         nix_path: nixpkgs=channel:nixos-unstable