[issue31938] Convert selectmodule.c to Argument Clinic

[Anthony Sottile]

Change by Anthony Sottile <asottile at umich.edu>:


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pull_requests: +20265
pull_request: https://github.com/python/cpython/pull/21098

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31938>
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