Bump actions/checkout from 5 to 6 (#483)

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/build-images.yml

@@ -19,7 +19,7 @@ jobs:
     name: ${{ matrix.tag }}-${{ matrix.distribution }}
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Lint Dockerfile
         uses: hadolint/hadolint-action@v3.2.0

.github/workflows/validate-readme.yml

@@ -15,7 +15,7 @@ jobs:
     name: validate
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
 
     - name: Validate README.md
       run: bash -c 'source helper-functions && validate_readme_constraints'