scheduled_messages: Send event on commit in edit_scheduled_message.

Earlier, we were using 'send_event' in 'edit_scheduled_messages'
which can lead to a situation, if any db operation is added after
the 'send_event' in future, where we enqueue events but the action
function fails at a later stage.

Events should not be sent until we know we're not rolling back.

Fixes part of #30489.

zerver/actions/scheduled_messages.py

@@ -127,6 +127,7 @@ def notify_update_scheduled_message(
     send_event_on_commit(user_profile.realm, event, [user_profile.id])
 
 
+@transaction.atomic(durable=True)
 def edit_scheduled_message(
     sender: UserProfile,
     client: Client,
@@ -138,7 +139,6 @@ def edit_scheduled_message(
     deliver_at: datetime | None,
     realm: Realm,
 ) -> None:
-    with transaction.atomic():
     scheduled_message_object = access_scheduled_message(sender, scheduled_message_id)
 
     # Handles the race between us initiating this transaction and user sending us the edit request.