Ensure NotificationRecipientService doesn't modify participants
What does this MR do?
In NotificationRecipientService
, we currently modify the memoised participants
on the target when adding watchers etc. I don't think this caused https://gitlab.com/gitlab-org/gitlab-ce/issues/19931#note_32488132, but it would be good to rule it out.
Are there points in the code the reviewer needs to double check?
Don't think so.
Why was this MR needed?
Modifying a memoised array when you don't intend to is a bad idea!