minor #12489 Update Configuring Symfony page (TheGarious)

This PR was merged into the 4.3 branch.

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Update Configuring Symfony page

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53d0ffd Update Configuring Symfony page

Author: javiereguiluz

configuration.rst

@@ -796,6 +796,8 @@ parameters at once by type-hinting any of its constructor arguments with the
 :class:`Symfony\\Component\\DependencyInjection\\ParameterBag\\ContainerBagInterface`::
 
     // src/Service/MessageGenerator.php
+    namespace App\Service;
+    
     // ...
 
     use Symfony\Component\DependencyInjection\ParameterBag\ContainerBagInterface;