Webhooks should not be triggered when no change is made
Related to: #19472 (closed), !5071 (merged)
Currently if we PUT /gitlab-org/gitlab-ce/issues/1234.json
with an array of issue[label_ids][]
identical to the labels already assigned to an issue, it will erroneously trigger web hooks. There should be a check to determine whether the issue has in fact been changed in any meaningful way before triggering webhooks or other services. I'm not sure if this applies only to issue labels or more broadly to all PUT
requests on this endpoint, but thought should be given to where else this may be an issue (merge requests, etc.).