minor #14553 [EventDispatcher] [Event Dispatcher] Fix typo for __invoke() (jmsche)

This PR was submitted for the 5.x branch but it was merged into the 4.4 branch instead.

Discussion
----------

[EventDispatcher] [Event Dispatcher] Fix typo for __invoke()

Commits
-------

4129e8e [Event Dispatcher] Fix typo for __invoke()

Author: javiereguiluz

event_dispatcher.rst

@@ -122,7 +122,7 @@ listener class:
    the ``kernel.exception`` event);
 #. If that method is not defined either, try to call the ``__invoke()`` magic
    method (which makes event listeners invokable);
-#. If the ``_invoke()`` method is not defined either, throw an exception.
+#. If the ``__invoke()`` method is not defined either, throw an exception.
 
 .. note::