minor #9027 fix rst syntax (xabbuh)

This PR was merged into the 3.3 branch.

Discussion
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fix rst syntax

Commits
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c0c01d3 fix rst syntax

Author: javiereguiluz

reference/events.rst

@@ -243,7 +243,7 @@ response:
         $response = new Response('No Content', 204);
         $event->setResponse($response);
 
-    The status code sent to the client in the above example will be ``204`. If
+    The status code sent to the client in the above example will be ``204``. If
     ``$event->allowSuccessfulResponse()`` is omitted, then the kernel will set
     an appropriate status code based on the type of exception thrown.