[Windows] multiprocessing handle leak when child process is killed during startup/unpickling

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-01-19.18:24:16.409>
labels = ['type-bug', '3.8', '3.9', '3.10', 'library', 'OS-windows']
title = '[Windows] multiprocessing handle leak when child process is killed during startup/unpickling'
updated_at = <Date 2021-03-30.18:31:06.717>
user = 'https://github.com/dgrunwald'

bugs.python.org fields:

activity = <Date 2021-03-30.18:31:06.717>
actor = 'eryksun'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)', 'Windows']
creation = <Date 2021-01-19.18:24:16.409>
creator = 'dgrunwald'
dependencies = []
files = ['49751']
hgrepos = []
issue_num = 42968
keywords = []
message_count = 3.0
messages = ['385283', '385284', '385380']
nosy_count = 6.0
nosy_names = ['paul.moore', 'tim.golden', 'zach.ware', 'eryksun', 'steve.dower', 'dgrunwald']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42968'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10']