Merge pull request #26463 from ngoldbaum/add-nogil-ci

TST: add basic free-threaded CI testing

.github/workflows/linux.yml

@@ -287,3 +287,25 @@ jobs:
         rm -rf build-install
         ./vendored-meson/meson/meson.py install -C build --destdir ../build-install --tags=runtime,python-runtime,devel
         python tools/check_installed_files.py $(find ./build-install -path '*/site-packages/numpy') --no-tests
+
+  free-threaded:
+    needs: [smoke_test]
+    runs-on: ubuntu-latest
+    if: github.event_name != 'push'
+    steps:
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
+      with:
+        submodules: recursive
+        fetch-tags: true
+    # TODO: replace with setup-python when there is support
+    - uses: deadsnakes/action@6c8b9b82fe0b4344f4b98f2775fcc395df45e494 # v3.1.0
+      with:
+          python-version: '3.13-dev'
+          nogil: true
+    # TODO: remove cython nightly install when cython does a release
+    - name: Install nightly Cython
+      run: |
+        pip install git+https://github.com/cython/cython
+    - uses: ./.github/meson_actions
+      env:
+        PYTHON_GIL: 0