Better feedback when adding a merge request dependency fails
The following discussion from !16799 should be addressed:
- [ ] @pedroms started a [discussion](https://gitlab.com/gitlab-org/gitlab/merge_requests/16799#note_225108426): (+2 comments)
> @igor.drozdov I wasn't able to reproduce any of the error states above: no error message and no MR is added as dependent.
issue