`catch_warnings` context manager causes all warnings to be printed every time, even after exiting

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-02-27.22:29:56.490>
labels = ['type-bug', 'library']
title = '`catch_warnings` context manager causes all warnings to be printed every time, even after exiting'
updated_at = <Date 2021-04-02.21:55:37.433>
user = 'https://github.com/gerritholl'

bugs.python.org fields:

activity = <Date 2021-04-02.21:55:37.433>
actor = 'taldcroft'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-02-27.22:29:56.490>
creator = 'Gerrit.Holl'
dependencies = []
files = []
hgrepos = []
issue_num = 29672
keywords = ['patch']
message_count = 10.0
messages = ['288677', '288678', '288680', '288709', '298588', '298822', '320662', '321380', '321393', '390103']
nosy_count = 6.0
nosy_names = ['pitrou', 'Gerrit.Holl', 'erik.bray', 'serhiy.storchaka', 'Segev Finer', 'taldcroft']
pr_nums = ['8232']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29672'
versions = []