Issue #16711: Fix required method names for collections.Iterator

Thanks to Inada Naoki

Doc/library/collections.rst

@@ -1057,7 +1057,7 @@ ABC                        Inherits from          Abstract Methods        Mixin
 
 .. class:: Iterator
 
-   ABC for classes that provide the :meth:`__iter__` and :meth:`next` methods.
+   ABC for classes that provide the :meth:`__iter__` and :meth:`__next__` methods.
    See also the definition of :term:`iterator`.
 
 .. class:: Sequence