Fix title underline length and use statement order

Author: lacatoire

messenger.rst

@@ -957,7 +957,7 @@ If you don't want to reset the container, add the ``--no-reset`` option when
 running the ``messenger:consume`` command.
 
 Custom Message Execution Strategy
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 .. versionadded:: 8.1
 
@@ -969,8 +969,8 @@ You can customize how messages are executed by implementing
 :class:`Symfony\\Component\\Messenger\\Execution\\MessageExecutionStrategyInterface`
 and passing it to the ``Worker`` constructor::
 
-    use Symfony\Component\Messenger\Execution\MessageExecutionStrategyInterface;
     use Symfony\Component\Messenger\Envelope;
+    use Symfony\Component\Messenger\Execution\MessageExecutionStrategyInterface;
 
     class MyCustomExecutionStrategy implements MessageExecutionStrategyInterface
     {