The check to see if we have no weakrefs isn't correct

[DinoV]

Bug report

Bug description:

https://github.com/python/cpython/blob/main/Objects/weakrefobject.c#L991

This is checking if we have a list at all, rather than if the list is empty. This is causing a slow down that's pretty significant on free-threaded builds

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-118519: Fix empty weakref list check #118520