minor #18025 [EventDispatcher] Update event_dispatcher.rst (danieleambrosino)

This PR was submitted for the 6.2 branch but it was merged into the 5.4 branch instead.

Discussion
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[EventDispatcher] Update event_dispatcher.rst

Fix a little spelling mistake.

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Commits
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6b7e144 Update event_dispatcher.rst

Author: javiereguiluz

event_dispatcher.rst

@@ -61,7 +61,7 @@ The most common way to listen to an event is to register an **event listener**::
     }
 
 Now that the class is created, you need to register it as a service and
-notify Symfony that it is a event listener by using a special "tag":
+notify Symfony that it is an event listener by using a special "tag":
 
 .. configuration-block::