[issue28533] Replace asyncore/asynchat/smptd in tests

[STINNER Victor]

Change by STINNER Victor <vstinner at python.org>:


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keywords: +patch
pull_requests: +27771
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/29521

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<https://bugs.python.org/issue28533>
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