[issue38435] Start the deprecation cycle for subprocess preexec_fn

[Gregory P. Smith]

Change by Gregory P. Smith <greg at krypto.org>:


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pull_requests: +22786
pull_request: https://github.com/python/cpython/pull/23936

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue38435>
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