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

[Roundup Robot]

Change by Roundup Robot <devnull at psf.upfronthosting.co.za>:


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nosy: +python-dev
nosy_count: 11.0 -> 12.0
pull_requests: +23895
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/25148

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