Update messenger.rst

Co-authored-by: Mata <[email protected]>

Author: sylfabre

messenger.rst

@@ -440,6 +440,7 @@ With the following code and configuration, messages will be dispatched like this
 * ``SmsNotification`` to ``async_2``
 
 .. code-block::php
+
     namespace App\Message;
 
     class SmsNotification extends Notification {}