build(deps): bump docker/build-push-action from 2.8.0 to 2.9.0

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 2.8.0 to 2.9.0.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v2.8.0...v2.9.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/container-image.yml

@@ -21,7 +21,7 @@ jobs:
     # https://github.com/marketplace/actions/build-and-push-docker-images
     # > The commit history is not preserved.
     # https://docs.docker.com/engine/reference/commandline/build/#git-repositories
-    - uses: docker/build-push-action@v2.8.0
+    - uses: docker/build-push-action@v2.9.0
       with:
         build-args: |
           SETUPTOOLS_SCM_PRETEND_VERSION=0 # git history unavailable (see above)