Add _waiters type hints to asyncio.locks

[Olegt0rr]

There's no public vars can be used to check Lock has waiters or not...
But it has _waiters

But my editor, used typedshed and says: Unresolved attribute reference '_waiters' for class 'Lock'

Also Semaphore already has _waiters type hint...

typeshed/stdlib/asyncio/locks.pyi

Lines 84 to 86 in 26452a7

	class Semaphore(_ContextManagerMixin, _LoopBoundMixin):
	_value: int
	_waiters: deque[Future[Any]]

But it has wrong type. It should be Optional, cause it's None on init: