Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
This was three issues combining:
approvals_before_merge param to editing an existing MR as there was for creating a new MR. This meant that creating a new MR with the same number of approvers as the target project, editing it, not changing anything, and clicking Save would produce a validation error.
set_suggested_approvers wasn't called in a couple of places where we render the MR edit form (like the above).
approvals_before_merge param was based on the source project, not the target project (unlike the model validation).