fix(ci): build free-threaded 3.14 wheels with cp314t ABI to stop upload collision

[antonwolfy]

The Python 3.14 conda/wheel build matrix intended to produce two variants — GIL-enabled (cp314) and free-threaded (cp314t) — but both entries actually built the same GIL interpreter. This caused the free-threading upload job to fail with a conflict, and meant no free-threaded package was ever produced.

The matrix used an empty python_spec for the entry it labeled 3.14t (free-threading), relying on a bare conda build -- python 3.14 to select the free-threaded interpreter:

python: ['3.10', '3.11', '3.12', '3.13', '3.14']
python_spec: ['']
include:
  - python: '3.14'
    python_spec: '3.14.* *_cp314'   # GIL

But in conda-forge, free-threading is opt-in only — it is not the default build for a bare python=3.14:

• Per PEP 779, 3.14 free-threading is "officially supported but still optional" (Phase II); making it the default is deferred to a future PEP (Phase III).
• The conda-forge global pinning matrix lists only the GIL ABI (*_cp314) as the default python variant; the free-threaded ABI (*_cp314t) must be requested explicitly.

So --python 3.14 resolved to the standard cp314 interpreter — identical to the explicit *_cp314 entry. Both jobs emitted a cp314-cp314 wheel with the same filename, colliding on upload.

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[github-actions]

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[coveralls]

coverage: 74.579%. remained the same — proper-enabling-free-threading-python-in-ci into master