[issue45678] `functools.singledispatchmethod` is missing tests (and is buggy in 3.9)

[miss-islington]

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


----------
pull_requests: +27677
pull_request: https://github.com/python/cpython/pull/29424

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue45678>
_______________________________________