Restrict access to release branches for LTS Refresh. BUG=b/529917915 Change-Id: I01be5fb11fdada53ddcf09191d638b7aed0c3394 Reviewed-on: https://cos-review.googlesource.com/c/All-Projects/+/166246 Tested-by: Derek Taylor <ddtaylor@google.com> Reviewed-by: Angel Adetula <angeladetula@google.com>