`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

logging.shutdown() のエントリーポイントから始め、logging._handlerList がどのように処理されるかを調べます。これには、報告で説明されている flush() と close() の繰り返し呼び出しも含まれます。shutdown が処理後にデフォルトのハンドラーリストをクリアすることを確認し、shutdown を繰り返し呼び出しても同じハンドラーが再度処理されないことを検証します。