ABCMeta.__subclasscheck__() doesn't support duck typing.

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-08-06.06:56:59.358>
labels = ['type-bug', 'library', '3.9', '3.10']
title = "ABCMeta.__subclasscheck__() doesn't support duck typing."
updated_at = <Date 2021-08-06.06:56:59.358>
user = 'https://bugs.python.org/grahamd'

bugs.python.org fields:

activity = <Date 2021-08-06.06:56:59.358>
actor = 'grahamd'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2021-08-06.06:56:59.358>
creator = 'grahamd'
dependencies = []
files = []
hgrepos = []
issue_num = 44847
keywords = []
message_count = 1.0
messages = ['399060']
nosy_count = 1.0
nosy_names = ['grahamd']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44847'
versions = ['Python 3.9', 'Python 3.10']