Fix typo in collections.abc docs example (#113310)

Calling the instance reference arg for the __next__ method, "next", seems misleading as it would normally just be "self"

Author: lbt

Doc/library/collections.abc.rst

@@ -87,7 +87,7 @@ the required methods (unless those methods have been set to
 
     class E:
         def __iter__(self): ...
-        def __next__(next): ...
+        def __next__(self): ...
 
 .. doctest::