minor #16520 [Messenger] Fix broken link to DoctrineReceiver in 6.0 (AymDev)

This PR was submitted for the 6.0 branch but it was merged into the 5.4 branch instead.

Discussion
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[Messenger] Fix broken link to DoctrineReceiver in 6.0

Came across a broken link to the `DoctrineReceiver` class when building my Azure transport.

Commits
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2036790 Fix broken link to DoctrineReceiver in Messenger

Author: javiereguiluz

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
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