Author-run commands now require a fork pull request

By default, update, rebase, squash and refresh can be run by anyone with write access, or by the pull request author. The author part now only applies to pull requests coming from a fork.

GitHub lets a user with read-only access open a pull request between two branches of a repository they cannot write to. The old default let that user have Mergify rewrite the head branch for them. On a fork the head branch is outside your repository, so the author case that this rule exists for is unchanged.

If you set commands_restrictions for these commands yourself, nothing changes.