[3.13] GH-91636: Clear weakrefs created by finalizers. (GH-136401)

[sergey-miryanov]

Weakrefs to unreachable garbage that are created during running of finalizers need to be cleared. This avoids exposing objects that have tp_clear called on them to Python-level code. (cherry picked from commit b6b99bf)

• Issue: Assertion failure when func_repr is called on an already tp_clear-ed object #91636

[gpshead]

I think this needs re-applying to 3.14 if we're going to do it for 3.13. it was removed (likely temporarily) from 3.14 as a risk mitigation for 3.14.1 (see issue and prs)