Bump actions/checkout from 5 to 6 (#28)

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

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -26,11 +26,11 @@ jobs:
       # the order of the checkout actions is important because all contents of
       # the target folder of the checkout action is removed
       - name: 'Clone the Example package'
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           repository: gap-packages/example
       - name: 'Check out this repository'
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           path: this-action/
       - uses: gap-actions/setup-gap@v3