Clarify that RecoverableMessageHandlingException retryDelay is milliseconds

Author: melkamar

messenger.rst

@@ -1203,7 +1203,7 @@ and must be retried. If you throw
 :class:`Symfony\\Component\\Messenger\\Exception\\RecoverableMessageHandlingException`,
 the message will always be retried infinitely and ``max_retries`` setting will be ignored.
 
-You can define a custom retry delay (e.g., to use the value from the ``Retry-After``
+You can define a custom retry delay in milliseconds (e.g., to use the value from the ``Retry-After``
 header in an HTTP response) by setting the ``retryDelay`` argument in the
 constructor of the ``RecoverableMessageHandlingException``.