Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     name: Validate a Pull Request
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Run yamllint
         uses: ibiqlik/action-yamllint@v3.1
@@ -36,11 +36,11 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           path: action
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           repository: ${{ matrix.repo-owner }}/${{ matrix.repo-name }}
           path: ${{ matrix.repo-name }}