minor #16979 [Security] Update security.rst (mohamedGasmii)

This PR was merged into the 4.4 branch.

Discussion
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[Security] Update security.rst

Fixing display php code block

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Commits
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0b546b1 [Security] Update security.rst

Author: javiereguiluz

security.rst

@@ -930,7 +930,7 @@ Next, you'll 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;