Bump actions/checkout from 3 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...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/dockerpublish.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v3
+        uses: actions/checkout@v6
 
       - name: Log in to the Container registry
         uses: docker/login-action@65b78e6e13532edd9afa3aa52ac7964289d1a9c1