Fixes issus #13382

[InFiNiTy0639]

Fixing Type Annotation for lock in Handler class

The type annotation for the lock attribute in the Handler class was previously incorrectly defined as threading.Lock | None in the typeshed stub. This is inconsistent with the CPython implementation, which uses threading.RLock (a reentrant lock) instead of a simple lock.

Changes made:

• Updated the type annotation for the lock attribute in the Handler class from threading.Lock | None to threading.RLock | None.
• This change aligns the typeshed stub with the actual implementation in CPython, where RLock is used instead of Lock.

Reasoning:

• The CPython source code (from version 2.5 onward) uses threading.RLock instead of threading.Lock for the lock attribute in the Handler class.
• RLock is not a subclass of Lock, so using Lock in the typeshed definition was incorrect.
• This update ensures the correct typing is reflected and avoids confusion when using static analysis tools or type checkers.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[JelleZijlstra]

I don't think the comment needs to be changed.

[InFiNiTy0639]

Ok 👍🙂