Merge branch 'rs-issue-1773' into 'master'
Fix mentions not being created upon issue/merge request update New cross-references weren't being added when they were made in an issue or merge request update. This happened because the relevant `UpdateService`s were making the `notice_added_references` call after the model had already been updated and saved, so the `changes` attribute was empty and no cross-references were made at all. This fixes the bug and adds a bit of testing and a bit of refactoring. Closes #1773 See merge request !974