fix: PYBIND11_INTERNALS_VERSION bump for MSVC

[rwgk]

Description

Piggy-backed on PR #4779. See comments there.

Suggested changelog entry:

Also bump ``PYBIND11_INTERNALS_VERSION`` for MSVC, which unlocks two new features without creating additional incompatibilities.

[henryiii]

Since we have to¹ bump this for MSVC anyway, would it make sense to go head and bump everything to 5? Or would it be better to use this as a testing ground, to see how many Windows users are affected by a bump?

Footnotes

1. Bump meaning these are no longer cross-compatible anyway. ↩

[rwgk]

Since we have to1 bump this for MSVC anyway, would it make sense to go head and bump everything to 5?

Good question, that crossed my mind, too. I think it would be much more straightforward to say "2.12 unconditionally uses 5". What I don't know: how much trouble will that cause for the community at large? Who feels strongly about making the call one way or another? I'm fine either way, happier with using 5 universally.

I do believe though that we should merge this PR straightaway, because holding it back while we make up our minds doesn't do any good for anyone.

[henryiii]

What I don't know: how much trouble will that cause for the community at large?

I don't know. I don't really have a feel for this. I know PyTorch uses this, but they disable our protections for cross-compilers, since they want to mix and match compilers. CUDA users sometimes disable those too, since they want to mix and match a CUDA compiler with a host compiler.

I do believe though that we should merge this PR straightaway, because holding it back while we make up our minds doesn't do any good for anyone.

Yes, but it was draft. :)

[rwgk]

Sorry I simply forgot to mark it as ready for review before.

[henryiii]

This already is incompatible with previous versions, due to the previous PR. So an easy change.