[3.13] gh-137017: Ensure `Thread.is_alive()` only returns False after the underlying OS thread exits (gh-137315)#138917

colesbury merged 2 commits intopython:3.13python/cpython:3.13from

miss-islington:backport-aa9ceb1-3.13miss-islington/cpython:backport-aa9ceb1-3.13Copy head branch name to clipboard