Cannot push outside of the GItLab UI to projects fork branches from a MR with "Allow edits from maintainers" set on.

Summary

In a MR from a fork, even with "Allow edits from maintainer" setting on, one cannot push changes to the fork's branch.

However, from the GitLab UI, it;s possible to rebase, and the widget correctly shows that the setting is on. So I guess there is missing some checks for the non GitLab UI case.

Steps to reproduce

• Contributor creates fork, say, whs/nautilus from a project in GNOME/nautilus
• Contributor makes some modification in the master branch of the fork
• Contributor creates a MR to GNOME/nautilus with the changes in whs/nautilus
• Sets the "Allow edits from maintainers" in the MR
• Maintainer of GNOME/nautilus fetchs the master branch from whs/nautilus following the instructions in GitLab UI.
• Maintainer creates some change
• Maintainer tries to push to whs/nautilus master branch doing (in the case of Nautilus): 'git push git@gitlab.gnome.org:whs/nautilus.git master'

What is the current bug behavior?

Here GitLab prevents the pushing.

What is the expected correct behavior?

GitLab doesn't prevent the pushing for fork branches that are part of a MR with the edit from maintainers on.