unittest.TestCase is not multiple-inheritance cooperative

Bug report

Bug description:

unittest's TestCase does not call super().__init__() which breaks cooperative multiple inheritance.

I would be happy to add this, but I can imagine someone somewhere relies on cooperative multiple inheritance not working.

CPython versions tested on:

3.11, 3.12, 3.13, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-125287

從 unittest.TestCase 的初始化開始，並在 CPython 上重現合作式多重繼承的情況。檢查其在所回報 Python 版本中的行為，並找出相關的 unittest 測試。完成的標準是：TestCase 能夠與多重繼承合作而不破壞現有的初始化行為，並有一個涵蓋該情況的回歸測試。