chore(deps): bump actions/checkout from 2 to 4 (#29)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/macos.yml

@@ -12,7 +12,7 @@ jobs:
       matrix:
         os: [macos-latest, macos-11]
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - uses: ./
       with:
         cvmfs_repositories: 'sft.cern.ch'