minor symfony#20181 [Mailer] Remove unnecessary type checking for the…

… method from SentMessageEvent (wkania)

This PR was merged into the 6.4 branch.

Discussion
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[Mailer] Remove unnecessary type checking for the method from SentMessageEvent

The getMessage method has been returning **only** SentMessage from the very [beginning](https://github.com/symfony/symfony/pull/47080/files#diff-19459911f97144033a370e7d86ae4e3bab9833c03cfe42e1eb3d71da90b15097R26).

Commits
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2bbdc99 Remove unnecessary type checking for the method from SentMessageEvent

mailer.rst

@@ -1728,14 +1728,10 @@ which is useful for debugging errors::
 
     use Symfony\Component\EventDispatcher\EventSubscriberInterface;
     use Symfony\Component\Mailer\Event\SentMessageEvent;
-    use Symfony\Component\Mailer\SentMessage;
 
     public function onMessage(SentMessageEvent $event): void
     {
         $message = $event->getMessage();
-        if (!$message instanceof SentMessage) {
-            return;
-        }
 
         // do something with the message
     }