Merge branch 'francoisrose/2024-11-22-empty-changes-mr-webhooks' into 'master'

Warn that `changes` can be empty in MR webhooks

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/173563



Merged-by: Amy Qualls <aqualls@gitlab.com>
Approved-by: Amy Qualls <aqualls@gitlab.com>
Co-authored-by: François Rosé <frose@gitlab.com>

doc/user/project/integrations/webhook_events.md

@@ -865,6 +865,10 @@ Merge request events are triggered when:
 - A commit is added in the source branch.
 - All threads are resolved on the merge request.
 
+Merge request events can be triggered even if the `changes` field is empty.
+Webhook receivers should always inspect the content of the `changes` field for the
+actual changes in a merge request.
+
 The available values for `object_attributes.action` in the payload are:
 
 - `open`