[github] bump docker/build-push-action from 4 to 6 (#21)

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 4 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v4...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]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/buildx.yaml

@@ -106,7 +106,7 @@ jobs:
         if [[ -f hooks/pre_build ]]; then ./hooks/pre_build; fi
 
     - name: Build and push
-      uses: docker/build-push-action@v4  # See https://github.com/docker/build-push-action
+      uses: docker/build-push-action@v6  # See https://github.com/docker/build-push-action
       with:
         context: ${{ env.WORKING_DIRECTORY }}
         labels: |