deps(actions): bump actions/checkout from 4 to 6 (#75)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Commits](https://github.com/actions/checkout/compare/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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/sync-about.yml

@@ -72,7 +72,7 @@ jobs:
       # any fix-up commit we make goes onto the PR branch itself. On
       # push events we check out the default ref. fetch-depth: 0 lets
       # us push back without "shallow update not allowed".
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
           ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.ref || github.ref }}

.github/workflows/sync-metadata.yml

@@ -14,7 +14,7 @@ jobs:
     name: metadata audit
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-python@v5
         with:
           python-version: "3.12"