Use constant to call event name

Author: cedriclombardot

doctrine/events.rst

@@ -266,8 +266,9 @@ a Doctrine entity listener in your application:
         // ...
         use App\Entity\User;
         use Doctrine\Bundle\DoctrineBundle\Attribute\AsEntityListener;
+        use Doctrine\ORM\Events;
 
-        #[AsEntityListener(event: 'postUpdate',  method: 'postUpdate', entity: User::class)]
+        #[AsEntityListener(event: Events::postUpdate, method: 'postUpdate', entity: User::class)]
         class UserChangedNotifier
         {
             // ...