minor #11945 Fixed broken build (Nyholm)

This PR was submitted for the master branch but it was squashed and merged into the 4.3 branch instead (closes #11945).

Discussion
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Fixed broken build

We are missing the version number to  `versionadded`.

FYI @javiereguiluz

Commits
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075b1cc Fixed broken build

Author: javiereguiluz

event_dispatcher.rst

@@ -67,7 +67,7 @@ The most common way to listen to an event is to register an **event listener**::
     Check out the :doc:`Symfony events reference </reference/events>` to see
     what type of object each event provides.
 
-.. versionadded::
+.. versionadded:: 4.3
 
     The :class:`Symfony\\Component\\HttpKernel\\Event\\ExceptionEvent` class was
     introduced in Symfony 4.3. In previous versions it was called

setup.rst

@@ -154,7 +154,6 @@ Go Deeper with Setup
     :glob:
 
     setup/homestead
-    setup/built_in_web_server
     setup/web_server_configuration
     setup/*