gh-135755: Document the new `PyFunction_GET_BUILTINS` macro by ZeroIntensity · Pull Request #135934 · python/cpython

That looks like it's used in a test -- the test assumes that it's working?
Yeah, the more I look into it, the better making it private seems.

cc @ericsnowcurrently, who added PyFunction_GET_BUILTINS in #133128