bug #12532 [Doctrine] Fix wrong event class for entity listener in example (sadikoff)

This PR was submitted for the master branch but it was merged into the 4.3 branch instead (closes #12532).

Discussion
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[Doctrine] Fix wrong event class for entity listener in example

Using class `PreUpdateEventArgs` in code example causes an exception:

>Argument 2 passed to App\EventListener\UserChangedNotifier::postUpdate() must be an instance of Doctrine\ORM\Event\PreUpdateEventArgs, instance of Doctrine\ORM\Event\LifecycleEventArgs given, called in .../vendor/doctrine/orm/lib/Doctrine/ORM/Event/ListenersInvoker.php on line 112

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Commits
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c5be930 Fix Doctrine Entity Listeners event class

Author: weaverryan

doctrine/events.rst

@@ -233,13 +233,13 @@ define a listener for the ``postUpdate`` Doctrine event::
     namespace App\EventListener;
 
     use App\Entity\User;
-    use Doctrine\ORM\Event\PreUpdateEventArgs;
+    use Doctrine\Common\Persistence\Event\LifecycleEventArgs;
 
     class UserChangedNotifier
     {
         // the entity listener methods receive two arguments:
         // the entity instance and the lifecycle event
-        public function postUpdate(User $user, PreUpdateEventArgs $event)
+        public function postUpdate(User $user, LifecycleEventArgs $event)
         {
             // ... do something to notify the changes
         }