[issue37788] fix for bpo-36402 (threading._shutdown() race condition) causes reference leak

[hai shi]

Change by hai shi <shihai1991 at 126.com>:


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nosy: +shihai1991
nosy_count: 12.0 -> 13.0
pull_requests: +23963
pull_request: https://github.com/python/cpython/pull/25226

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue37788>
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