ci: run the free-threaded and typing jobs on the matrix's Python

[pylaterreur]

The free-threaded test jobs and the typing jobs don't run on the Python they're named after.

test.yml. uv 0.8.11, the pinned version, only uses a free-threaded interpreter when one is requested explicitly (e.g. 3.14t; uv 0.9 relaxed this for 3.14+). uv run only requests >=3.10 from requires-python. So in the t jobs, uv skips the interpreter that setup-python installed:

DEBUG Skipping interpreter at `/opt/hostedtoolcache/Python/3.14.8/x64-freethreaded/bin/python3` from first executable in the search path: does not satisfy request `>=3.10`
Using CPython 3.12.3 interpreter at: /usr/bin/python3

None of the 14 t jobs in main's scheduled run 38940387418 used a free-threaded interpreter:

jobs	interpreter uv used instead
ubuntu-24.04 and ubuntu-24.04-arm, 3.13t and 3.14t	/usr/bin/python3 (3.12.3)
macos-26, 3.13t and 3.14t	/opt/homebrew/opt/python@3.15/bin/python3.15 (3.15.0)
macos-26-intel, 3.13t / 3.14t	/usr/local/bin/python3 (3.13.16 / 3.14.8)
windows-2022 (x64 and x86), 3.13t and 3.14t	...\Python\3.12.10\x64\python3.exe
windows-11-arm, 3.13t and 3.14t	...\Python\3.13.16\arm64\python3.exe

With UV_PYTHON set to the matrix version, uv uses the interpreter installed by setup-python. The other jobs already end up on that interpreter, and this keeps them there.

typing.yml. The workflow has no setup-python step and never passes matrix.py to uv. All 7 mypy jobs therefore run on the runner's /usr/bin/python3 (3.12.3) (run 38941189455). Like test.yml, it now installs the matrix version with setup-python and sets UV_PYTHON.

This also affects the 3.15t jobs that #357 adds: its fork run of test (ubuntu-24.04, 3.15t, x64) ran on /usr/bin/python3 (3.12.3).

Testing. I ran this branch on my fork:

• test.yml: all 14 t jobs now run on python3.13t/python3.14t (Linux x64/arm64, macOS arm64/x64, Windows x64/x86/arm64).
  • The C backend passes in all of them (292 passed), and the CFFI backend passes on 3.14t (266 passed, 26 skipped).
  • The Rust step still has its known test_optimize failure.
  • The one failed job, macos-26-intel, 3.10, ran into hypothesis's 20 s deadline in a fuzzing test. That also happens on main (scheduled run 38780348047), and ci: fix the anaconda, wheel, external-zstd and flaky test workflows #358 removes that deadline.
• typing.yml: every job runs mypy on its matrix Python, from 3.10.22 to 3.14.8 including python3.13t and python3.14t. All 7 pass.

I also reproduced the problem locally with uv 0.8.11 and GitHub's 3.15.0t build first on PATH. uv run --locked picks /usr/bin/python3 (Py_GIL_DISABLED = 0). With UV_PYTHON=3.15t, it picks python3.15t (Py_GIL_DISABLED = 1). zizmor 1.31.1 (offline audits) and actionlint report nothing.

Prepared with the help of Claude Code.

🤖 Generated with Claude Code