Bump docker/build-push-action from 4 to 6 (#2100)

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](https://github.com/docker/build-push-action/compare/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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/workflow.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
     - uses: actions/checkout@v3
     - name: Build the Docker test image for tox
-      uses: docker/build-push-action@v4
+      uses: docker/build-push-action@v6
       with:
         file: tests/Dockerfile
         tags: rqtest-image:latest