Spec change: allow more precise gradual types than Any for ambiguous overload returns

* DPO thread: https://discuss.python.org/t/permitting-more-precise-inferred-types-from-ambiguous-overloads/108776
* Spec/conformance PR: https://github.com/python/typing/pull/2350

Approvals:

- [x] Carl
- [x] David
- [x] Jelle
- [x] Joren
- [ ] Rebecca
