[3.14] gh-115999: Note Python 3.14 free-threaded changes in What's New (gh-131285) (gh-133824)

gh-115999: Note Python 3.14 free-threaded changes in What's New (gh-131285)

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(cherry picked from commit f28cbc9fd3f37656ad55ef2488b65343b97fa902)

Co-authored-by: Donghee Na <donghee.na@python.org>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: T. Wouters <thomas@python.org>
Co-authored-by: mpage <mpage@cs.stanford.edu>