Bump docker/build-push-action from 3 to 6 (#725)

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 3 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v3...v6)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-version: '6'
  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/mpi-operator-docker-image-publish.yml

@@ -49,7 +49,7 @@ jobs:
         uses: docker/[email protected]
 
       - name: Build and push
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v6
         with:
           platforms: linux/amd64,linux/arm64,linux/ppc64le
           context: .