Experiment: Undo PR #5718 production code changes only, keep added test.

[rwgk]

Description

Experiment: Does the test added under PR #5718 fail anywhere without the production code changes?

Suggested changelog entry:

• Placeholder.

[rwgk]

@henryiii What's the trick to run the tests on all platforms?

[henryiii]

Take it out of draft.

[henryiii]

LINK : fatal error LNK1104: cannot open file 'python313t.lib' is unrelated, it's a bug in Python 3.13.4.

[rwgk]

@Rosdf Could you please help working on the new test, so that it fails without the production code changes?

The only one I'd worry about is:

    v_h.value_ptr() = const_cast<void *>(static_cast<const void *>(ptr));

FWIW, I would have guessed that the new test does not work without the production code changes. I was a bit surprised when my quick experiment showed that it doesn't.

[rwgk]

@Rosdf I forgot to add, to keep things simple, could you please open a new PR? (I don't think you can push to this one; unless I mess with permissions somehow.)

[Rosdf]

#5727