Follow-up from "Add `/relate` quick action to WorkItems"

The following discussion from !172901 (merged) should be addressed:

• @nicolasdular started a discussion: (+2 comments)

  I know we have a test here, but I tried to /relate a group level work item in the frontend and it didn't work for me. Same for @peanutandlevi /unlink MR. Is this just something on my instance or does it also not work for you?