When a user creates a backport PR using the /backport command, they are supposed to get push access to the branch in the fork repository. On GitHub, this doesn't seem to be working. All the backport branches in https://github.com/openjdk-bots/jdk21 have branch protection rules restricting who can push, but none contain any users in the allow list (except one which I manually modified for now).

This is handled by the method GitHubRepository::restrictPushAccess.