MNT: account for removed opcode in Python 3.16

[tacaswell]

This is probably too early to start worrying about this, but CPython removed this opcode in python/cpython#146314 / python/cpython@a3dc784

This is not the most elegant way of fixing this, but it kept the public API as stable as possible.

The tests pass in a py316 build. From a very quick skim of the code it looks like these globals are only used in one function and only used to get the names of things that are global. Given that upstream replaced the delete with push NULL and then store, I think that this will still work as intended.

Please feel free to treat this as an overly enthusiastic bug report rather than a PR 😄 .

[tacaswell]

(force-pushed because I decided I wanted this done with a different email address, the email + signing key are the only changes)

[lesteve]

Thanks for the PR 🙏!

Out of pure curiosity, how did you bump into this?

For context the CPython PR: python/cpython#146314. This is only in main right now, so indeed this is specific to CPython 3.16.

I double-checked sys.version_info < (3, 16) works for CPython built from main (I wasn't 100% sure off the top of my head 😅)

❯ ./python
Python 3.16.0a0 (heads/main:f715d25a8f0, Sep 10 2026, 08:12:53) [GCC 16.2.1 20260810] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.version_info < (3, 16)
False

I am not a cloudpickle maintainer, but I'll try get a cloudpickle developer to trigger the workflow and review the PR.