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/backport-prs.yml

@@ -27,7 +27,7 @@ jobs:
         startsWith(github.event.comment.body, '/backport')
       )
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Create backport pull requests
         uses: korthout/backport-action@v3
         with:

.github/workflows/build.yml

@@ -16,7 +16,7 @@ jobs:
 
     steps:
       - name: Checkout Repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Validate Gradle Wrapper
         uses: gradle/actions/wrapper-validation@v5