DRAFT: Add free threaded Python 3.14t to CI workflow matrix

[cclauss]

Continues the work started in:

• Add Python 3.14 to CI workflow matrix #49

Blocked by:

• Add Python 3.14, 3.14t, and PyPy-3.11 to the testing valkey-io/libvalkey-py#35
• A libvalkey-py release > v4.0.1 https://github.com/valkey-io/libvalkey-py/releases

Pytest warning:

=============================== warnings summary ===============================
:491
:491: RuntimeWarning: The global interpreter lock (GIL) has been enabled to load module 'libvalkey.libvalkey', 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.

Blocked by:

• Support for free-threaded Python google/brotli#1241
• Test Python thread safety with pytest-run-parallel valkey-io/libvalkey-py#42