bump symfony to 5.4.21

adapt to the new EventDispatcher API
  - Symfony\Component\EventDispatcher => Symfony\Contracts\EventDispatcher
  - dispatch() arguments swap
  - execute() must return int

app/Job/TaskLinkEventJob.php

@@ -38,7 +38,7 @@ class TaskLinkEventJob extends BaseJob
             ->buildEvent();
 
         if ($event !== null) {
-            $this->dispatcher->dispatch($eventName, $event);
+            $this->dispatcher->dispatch($event, $eventName);
         }
     }
 }