isinstance accepts subtypes of tuples as second argument

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-02-04.18:30:00.188>
labels = ['type-bug', '3.9']
title = 'isinstance accepts subtypes of tuples as second argument'
updated_at = <Date 2020-02-04.21:31:43.493>
user = 'https://github.com/ewjoachim'

bugs.python.org fields:

activity = <Date 2020-02-04.21:31:43.493>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2020-02-04.18:30:00.188>
creator = 'ewjoachim'
dependencies = []
files = ['48884']
hgrepos = []
issue_num = 39550
keywords = []
message_count = 4.0
messages = ['361362', '361363', '361365', '361371']
nosy_count = 4.0
nosy_names = ['vstinner', 'serhiy.storchaka', 'p-ganssle', 'ewjoachim']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39550'
versions = ['Python 3.9']