[3.12] gh-127750: Backport some tests for singledispatchmethod (GH-130309) (GH-130340)#130341

serhiy-storchaka merged 2 commits intopython:3.12python/cpython:3.12from

miss-islington:backport-68c57d6-3.12miss-islington/cpython:backport-68c57d6-3.12Copy head branch name to clipboard