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](https://github.com/actions/checkout/compare/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>

.github/workflows/action.yml

@@ -15,7 +15,7 @@ jobs:
       actions: write
     steps:
       # checkout this repository
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       # prevent GitHub from suspending cronjob
       - uses: liskin/gh-workflow-keepalive@v1