[issue40692] Adjust test_concurrent_futures to run more of its tests if multiprocessing.synchronize is missing

[Roundup Robot]

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


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keywords: +patch
nosy: +python-dev
nosy_count: 4.0 -> 5.0
pull_requests: +19527
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20239

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40692>
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