Bump docker/build-push-action in the ci_dependencies group

Bumps the ci_dependencies group with 1 update: [docker/build-push-action](https://github.com/docker/build-push-action).


Updates `docker/build-push-action` from 6.7.0 to 6.8.0
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@5cd11c3...32945a3)

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

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

.github/workflows/release-50_publish-docker.yml

@@ -322,7 +322,7 @@ jobs:
 
       - name: Build and push
         id:   docker_build
-        uses: docker/build-push-action@5cd11c3a4ced054e52742c5fd54dca954e0edd85 #  v6.7.0
+        uses: docker/build-push-action@32945a339266b759abcbdc89316275140b0fc960 #  v6.8.0
         with:
           push: true
           file: docker/dockerfiles/polkadot/polkadot_injected_debian.Dockerfile