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/hassfest.yaml

@@ -10,5 +10,5 @@ jobs:
   validate:
     runs-on: "ubuntu-latest"
     steps:
-      - uses: "actions/checkout@v5"
+      - uses: "actions/checkout@v6"
       - uses: home-assistant/actions/hassfest@master