Bump actions/checkout from 5 to 6

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>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
     env:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/${{ matrix.gemfile }}.gemfile
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Ruby ${{ matrix.ruby-version }}
         uses: ruby/setup-ruby@v1
         with: