gitlab-16.6: new unprotection logic necessary

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/136225 and/or https://gitlab.com/gitlab-org/gitlab/-/merge_requests/133268 changed branch protection logic where other project settings can influence whether it is actually protected or not. It seems that using the webpage to add and remove protection clears some state as well.

TODO:

• enhance the protected field in the API to indicate "protected by rules" or something
• add whatever logic to the director is needed to handle the problem as best it can
• add this situation to the end-to-end test (!362 (closed) enhances the existing unprotect case in e2e testing with the default branch bit at least)

Cc: @brad.king