MR widget is still showing "Allows edits from maintainers" after MR is merged
After an MR is merged, we still mention "Allows edits from maintainers" in the MR widget while we don't allow maintainers to push to the branch anymore. We should only show that message when the merge request is open.
Seen in https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/17815.