add $notificationId to every broadcast notification

app/Http/Controllers/EventsController.php

@@ -107,7 +107,8 @@ class EventsController extends Controller
                 foreach ($participants as $user) {
                     broadcast(new EventParticipationCancelled(
                         $user->id,
-                        $event
+                        $event,
+                        $notification->id,
                     ));
 
                     $data = [