use of uninitialized value with msan from subprocess_fork_exec

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-03-02.00:48:44.660>
labels = ['type-feature', 'library', '3.9', '3.10', '3.11']
title = 'use of uninitialized value with msan from subprocess_fork_exec'
updated_at = <Date 2022-03-02.00:48:44.660>
user = 'https://github.com/yilei'

bugs.python.org fields:

activity = <Date 2022-03-02.00:48:44.660>
actor = 'yilei'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-03-02.00:48:44.660>
creator = 'yilei'
dependencies = []
files = []
hgrepos = []
issue_num = 46899
keywords = []
message_count = 1.0
messages = ['414320']
nosy_count = 2.0
nosy_names = ['gregory.p.smith', 'yilei']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue46899'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']