Verify update of cloudbuild-test-*.yaml files in upcoming release #730

Part of #691

The release-please.yml file was updated to include these files (#728) while this release PR was already open . However, add the release-please:force-run label to PR 728 and 727 (as documented in https://github.com/googleapis/release-please/blob/main/README.md#step-3-rerun-release-please) and closing and re-opening the release PR didn't do the trick.

On the other hand, adding the cloudbuild.yaml file to the extra-files field in release-please.yaml with an inline annotation x-version-update:<artifact-name>:released worked.

Reference for both settings:

• https://github.com/googleapis/release-please/blob/main/docs/customizing.md#updating-arbitrary-files
• https://github.com/googleapis/release-please/blob/main/docs/java-releases.md