Update to release-please v16.15.0 for always-update

Support for the always-update argument was added in release-please v16.15.0 (https://github.com/googleapis/release-please/releases/tag/v16.15.0)

Any chance you can update to the latest release-please library from November of last year? We require linear history and up to date branches (this is actually to make sure we don't get race conditions in release please when the release please action hasn't run after a merge - i.e. a release is merged before the rp action has run for the latest commit). I would prefer to have the release please action be the only contributor to the release please branch - so the always-update is a perfect option for that.

I see there is a PR open already - https://github.com/googleapis/release-please-action/pull/1056. Then preferably a release for this action would be created.

Start with the release-please action dependency and the already-open PR #1056, then verify the release-please v16.15.0 support for the always-update argument. Done means updating the action to the requested release and creating a release for the action.

Written by the indexing model from the issue text.