ci: add free threaded Python 3.14t to test workflow

[cclauss]

https://hugovk.github.io/free-threaded-wheels

% uvx --with=fastexcel python3.14t -c "import fastexcel"

Built fastexcel==0.16.0
    Installed 1 package in 1ms
<frozen importlib._bootstrap>:491: RuntimeWarning: The global interpreter lock (GIL) has been enabled
to load module 'fastexcel._fastexcel', which has not declared that it can run safely without the GIL.
To override this behavior and keep the GIL disabled (at your own risk), run with PYTHON_GIL=0 or -Xgil=0.

[lukapeschke]

Hello and thank you for your contribution! Great initiative, I'll try to add free-threaded wheels asap 😄 Could you please update pyyaml , markupsafe and pandas to versions providing free-threaded wheels ? Building the dependencies slows down the CI process a lot