`logging.shutdown()` should clear `logging._handlerList` if that's what it's called with

Bug report

Bug description:

In the wild, I've encountered situations where logging.shutdown gets called more than once in a process.

The current implementation is called with logging._handlerList by default, meaning that handlers can have their flush() and close() methods called more than once, which can cause bad things to happen if those handlers are not amenable to being closed more than once.

If logging.shutdown() is processing logging._handlerList, it should clear that list once it finished to prevent handlers having their flush() and close() methods called more than once.

CPython versions tested on:

3.12, CPython main branch

Operating systems tested on:

Linux, macOS

Linked PRs

• gh-129681

從 logging.shutdown() 進入點開始，檢查它如何處理 logging._handlerList，包括報告中描述的對 flush() 和 close() 的重複呼叫。確認 shutdown 在處理預設處理常式清單後會清空該清單，並驗證重複呼叫 shutdown 不會再次處理相同的處理常式。