[3.14] gh-119132: Update 'Using Python on macOS' documentation. (GH-135591) (#135594)

Remove `experimental` qualification for free-threading in the document text. Note that images included in the document will be updated later in the release cycle.
(cherry picked from commit 7c685894cd9c2c669f09fad31365e3ad6c0c3861)

Co-authored-by: Ned Deily <nad@python.org>