ghactions: bump docker/build-push-action from 2.5.0 to 2.9.0

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 2.5.0 to 2.9.0.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@ad44023...7f9d37f)

---
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/backup-operator-docker.yml

@@ -41,7 +41,7 @@ jobs:
         uses: docker/metadata-action@98669ae865ea3cffbcbaa878cf57c20bbf1c6c38
         with:
           images: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}
-      - uses: docker/build-push-action@ad44023a93711e3deb337508980b4b5e9bcdc5dc
+      - uses: docker/build-push-action@7f9d37fa544684fb73bfe4835ed7214c255ce02b
         with:
           context: .
           push: true