Bump docker/build-push-action from 5 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 5 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v5...v6)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/publish.yml

@@ -43,15 +43,15 @@ jobs:
           username: coldfix
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
-      - uses: docker/build-push-action@v5
+      - uses: docker/build-push-action@v6
         with:
           platforms: linux/amd64
           build-args: FROM=certbot/certbot:latest
           load: true
           tags: |
             coldfix/certbot-dns-netcup:amd64-latest
             coldfix/certbot-dns-netcup:amd64-${{ github.ref_name }}
-      - uses: docker/build-push-action@v5
+      - uses: docker/build-push-action@v6
         with:
           platforms: linux/arm64
           build-args: FROM=certbot/certbot:arm64v8-latest