[docs] [issue17576] PyNumber_Index() is not int-subclass friendly (or operator.index() docos lie)

Change by Terry J. Reedy <tjreedy@udel.edu>: ---------- versions: +Python 3.10, Python 3.9 -Python 2.7, Python 3.3, Python 3.4 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue17576> _______________________________________