[BUG]: Python 3.14a7 breaks reference call policy test `test50_call_policy()`

[wjakob]

Problem description

Some change in the latest Python 3.14a7 version breaks something in a pretty complex testcase related to call policies. See, e.g., https://github.com/wjakob/nanobind/actions/runs/14372986244/job/40299390299. Tagging @oremanj who wrote this testcase. I must admit I don't really grasp what is happening and how it interacts with this testcase.

Reproducible example code

See https://github.com/wjakob/nanobind/actions/runs/14372986244/job/40299390299

[wjakob]

Humm, I see now that other tests are also failing, not just test50.

[wjakob]

I opened an issue in the Python tracker to ask for help: python/cpython#132346

[wjakob]

I bisected this to a specific commit/PR (python/cpython#130708), and it looks like this may be an intentional change.