Add Python 3.14 to text matrix

[kenodegard]

Description

Alternative to #5938

Fixing all of the tests is a larger effort so can we unblock adding Python 3.14 to the test matrix by marking failures as xfail/skip? Will open issue to tackle refactoring those in later PRs.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

Merging this PR will not alter performance

✅ 5 untouched benchmarks

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_{Comparing kenodegard:python314-skip (bdf6e31) with main (f4d0adf)¹}

Footnotes

1. No successful run was found on main (bf30c6a) during the generation of this report, so f4d0adf was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[jezdez]

I think this is reasonable!