Fix broken link to DoctrineReceiver in Messenger

Updates the FQCN for DoctrineReceiver as the class moved in a Bridge namespace after Symfony 6.0

Author: AymDev

messenger/custom-transport.rst

@@ -127,7 +127,7 @@ Here is a simplified example of a database transport::
 The implementation above is not runnable code but illustrates how a
 :class:`Symfony\\Component\\Messenger\\Transport\\TransportInterface` could
 be implemented. For real implementations see :class:`Symfony\\Component\\Messenger\\Transport\\InMemoryTransport`
-and :class:`Symfony\\Component\\Messenger\\Transport\\Doctrine\\DoctrineReceiver`.
+and :class:`Symfony\\Component\\Messenger\\Bridge\\Doctrine\\Transport\\DoctrineReceiver`.
 
 Register your Factory
 ---------------------