What does this MR do?
Fix epic fullscreen editing
Are there points in the code the reviewer needs to double check?
Why was this MR needed?
Screenshots (if relevant)
Does this MR meet the acceptance criteria?
Changelog entry added, if necessary
Tests added for this feature/bug
Backport to CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/15437
Has been reviewed by Frontend
What are the relevant issue numbers?
Closes #4065 (closed)