unittest: tearDown is not called if asyncSetUp fails

In unittest.TestCase, tearDown() is always called if setUp() is successful. It is only not called when setUp() fails. In IsolatedAsyncioTestCase, which is a subclass of TestCase, tearDown() is not called if setUp() is successful, but asyncSetUp() fails. I think is a problem.

Linked PRs

• gh-99596

首先比较 unittest.TestCase 与 IsolatedAsyncioTestCase 的 setup 和 teardown 生命周期，重点关注 asyncSetUp() 失败时会发生什么。链接的 PR gh-99596 所引用的工作应包括：在 setUp() 成功后接着 asyncSetUp() 失败时执行 teardown，并提供回归测试覆盖。