Use `EnvironmentVarGuard` in tests instead of manually messing with `os.environ`

Feature or enhancement

Proposal:

Some tests manually tweak os.environ. There is new way to do that with EnvironmentVarGuard. Identify all places and update.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-128439
• gh-128476
• gh-128522
• gh-130002
• gh-131870

在 CPython 测试套件中搜索手动修改 os.environ 的测试，然后将这些用法与 EnvironmentVarGuard 进行比较。开始之前先查看链接的 PR（gh-128439、gh-128476、gh-128522、gh-130002 和 gh-131870）；当所有适用的手动环境更改都已迁移且受影响的测试通过时，工作就完成了。