[issue34805] Explicitly specify `MyClass.__subclasses__()` returns classes in definition order

[miss-islington]

Change by miss-islington <mariatta.wijaya+miss-islington at gmail.com>:


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nosy: +miss-islington
nosy_count: 7.0 -> 8.0
pull_requests: +22714
pull_request: https://github.com/python/cpython/pull/23850

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34805>
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