minor #18080 Update event_dispatcher.rst (hbgamra)

This PR was submitted for the 6.3 branch but it was merged into the 5.4 branch instead.

Discussion
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Update event_dispatcher.rst

Fix bug return type

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Commits
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0f23790 Update event_dispatcher.rst

Author: javiereguiluz

event_dispatcher.rst

@@ -255,7 +255,7 @@ listen to the same ``kernel.exception`` event::
 
     class ExceptionSubscriber implements EventSubscriberInterface
     {
-        public static function getSubscribedEvents()
+        public static function getSubscribedEvents(): array
         {
             // return the subscribed events, their methods and priorities
             return [