bug #19998 [Notifier] Fix code example for SentMessageEvent (jeremyjumeau)

This PR was merged into the 5.4 branch.

Discussion
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[Notifier] Fix code example for `SentMessageEvent`

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Commits
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429d700 fix: notifier code example for SentMessageEvent

Author: OskarStark

notifier.rst

@@ -892,7 +892,7 @@ is dispatched. Listeners receive a
 
     $dispatcher->addListener(SentMessageEvent::class, function (SentMessageEvent $event) {
         // gets the message instance
-        $message = $event->getOriginalMessage();
+        $message = $event->getMessage();
 
         // log something
         $this->logger(sprintf('The message has been successfully sent and has id: %s', $message->getMessageId()));