Avoid modifying the process global environment (not thread safe)

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-01-18.00:47:44.215>
labels = ['expert-subinterpreters', 'interpreter-core', '3.9', 'type-crash']
title = 'Avoid modifying the process global environment (not thread safe)'
updated_at = <Date 2021-04-16.00:43:07.242>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2021-04-16.00:43:07.242>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Interpreter Core', 'Subinterpreters']
creation = <Date 2020-01-18.00:47:44.215>
creator = 'gregory.p.smith'
dependencies = []
files = []
hgrepos = []
issue_num = 39376
keywords = []
message_count = 2.0
messages = ['360222', '360225']
nosy_count = 2.0
nosy_names = ['gregory.p.smith', 'eric.snow']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue39376'
versions = ['Python 3.9']