Add tests on basic `PyStackRef` functions

Feature or enhancement

Proposal:

Definitions of basic PyStackRef manipulation functions aren't so easy.
There are a lot of them, they have connections to each other and we have 3 variants of them now (GIL, no-GIL, PyStackRef debug).

It's easy to forget something when provide some change to them.
In fact, there is one of such issues for PyStackRef debug build: https://github.com/python/cpython/issues/135125

I propose to add tests that ensure all basic PyStackRef functions are correct in combination.

I've already have a PR.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-139717
• gh-141675
• gh-143024