[3.12] Fix typo in collections.abc docs example (GH-113310) (#113311)

Fix typo in collections.abc docs example (GH-113310)

Calling the instance reference arg for the __next__ method, "next", seems misleading as it would normally just be "self"
(cherry picked from commit 22b8945d7678be86f801ca54f004a5dba2006835)

Co-authored-by: David Greaves <david@dgreaves.com>