Update RuntimeException message when no data has been found (#51133)

src/Illuminate/Notifications/Channels/BroadcastChannel.php

@@ -70,6 +70,6 @@ protected function getData($notifiable, Notification $notification)
             return $notification->toArray($notifiable);
         }
 
-        throw new RuntimeException('Notification is missing toArray method.');
+        throw new RuntimeException('Notification is missing toBroadcast / toArray method.');
     }
 }