minor #17166 Trying to fix code sample syntax (ThomasLandauer)

This PR was merged into the 5.4 branch.

Discussion
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Trying to fix code sample syntax

Thanks to  `@alexislefebvre` at #17154 (comment)

Commits
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7261de9 Trying to fix code sample syntax

Author: xabbuh

security.rst

@@ -1746,7 +1746,7 @@ Next, you need to create a route for this URL (but not a controller):
             <route id="app_logout" path="/logout" methods="GET"/>
         </routes>
 
-    ..  code-block:: php
+    .. code-block:: php
 
         // config/routes.php
         use Symfony\Component\Routing\Loader\Configurator\RoutingConfigurator;