Namespaces: note that enums are affected (#4739)

Co-authored-by: Tim Düsterhus <timwolla@googlemail.com>

Author: DanielEScherzer

language/namespaces.xml

@@ -91,7 +91,8 @@ echo constant($d); // see "Namespaces and dynamic language features" section
   <?phpdoc print-version-for="namespaces"?>
   <para>
    Although any valid PHP code can be contained within a namespace, only the following
-   types of code are affected by namespaces: classes (including abstracts and traits), interfaces, functions and constants.
+   types of code are affected by namespaces: classes (including abstract classes, traits and enums), interfaces,
+   functions and constants.
   </para>
   <para>
    Namespaces are declared using the <literal>namespace</literal>