gh-90982: Say "Added the optional *prefixes* parameter"

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Doc/library/site.rst

@@ -252,7 +252,7 @@ Module contents
    .. versionadded:: 3.2
 
    .. versionchanged:: 3.3
-      Add the optional *prefixes* argument.
+      Added the optional *prefixes* parameter.
 
 
 .. function:: getuserbase()