minor #20364 [EventDispatcher] Fix XSS in example event dispatcher (nicolas-grekas)

This PR was merged into the 5.4 branch.

Discussion
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[EventDispatcher] Fix XSS in example event dispatcher

The exception message can contain unfiltered user input.

Commits
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2ff16f8 Fix XSS in example event dispatcher

Author: javiereguiluz

event_dispatcher.rst

@@ -41,6 +41,7 @@ The most common way to listen to an event is to register an **event listener**::
             // Customize your response object to display the exception details
             $response = new Response();
             $response->setContent($message);
+            $response->headers->set('Content-Type', 'text/plain; charset=utf-8');
 
             // HttpExceptionInterface is a special type of exception that
             // holds status code and header details