ci: Build free threaded wheels for python 3.14t rather than 3.13t

[aborgna-q]

As of April 2026, we suggest not enabling builds for Free-threaded Python 3.13 going forward. The 3.13t release was considered experimental, is approximately 30% slower in single-threaded performance than 3.14t, and does not include a number of safety fixes for builtins and the standard library that were included in 3.14t. Free-threaded 3.14 also has better ecosystem compatibility than 3.13.

(source)