MNT: add missing CPython 3.14 PyPI trove classifier - #18471

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Whoops, I forgot we didn't have ABI stability on these wheels yet. I'll move this to draft for now, it should probably be done at the same time that cibuildwheel is upgraded.

This now closes #18187

So just to be sure, this is ready for final review?

Yes

A bit of a shame this wasn't included in 7.1.1 despite Python 3.14 clearly being supported now. Could we backport this one now ? @astrofrog