Fix example code in docs (#4375)

Resources/doc/reference/batch_actions.rst

@@ -68,6 +68,7 @@ granularity), the passed query is ``null``.
     use Sonata\AdminBundle\Controller\CRUDController as BaseController;
     use Sonata\AdminBundle\Datagrid\ProxyQueryInterface;
     use Symfony\Component\HttpFoundation\RedirectResponse;
+    use Symfony\Component\HttpFoundation\Request;
     use Symfony\Component\Security\Core\Exception\AccessDeniedException;
 
     class CRUDController extends BaseController