test_socket leaks file descriptors on macOS

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-04-29.08:26:44.616>
labels = ['3.8', 'type-bug', 'library', '3.9', '3.10']
title = 'test_socket leaks file descriptors on macOS'
updated_at = <Date 2020-06-07.17:06:50.594>
user = 'https://github.com/tirkarthi'

bugs.python.org fields:

activity = <Date 2020-06-07.17:06:50.594>
actor = 'remi.lapeyre'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-04-29.08:26:44.616>
creator = 'xtreak'
dependencies = []
files = []
hgrepos = []
issue_num = 36750
keywords = []
message_count = 4.0
messages = ['341052', '341053', '341136', '370908']
nosy_count = 5.0
nosy_names = ['vstinner', 'giampaolo.rodola', 'pablogsal', 'remi.lapeyre', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36750'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']