CI: Try to build wheels for free threading

As per conda-incubator/setup-miniconda#395

The default should be the free-threadin version

Author: HaoZeke

.github/workflows/build.yml

@@ -19,7 +19,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-latest ]
-        python-version: [ 3.9, "3.10", "3.11" ]
+        python-version: [ 3.9, "3.10", "3.11", "3.13t" ]
 
     env:
       PYTHON_VERSION: ${{ matrix.python-version }}
@@ -54,7 +54,7 @@ jobs:
         # macos-13 runners have intel chips. macos-14 and above
         # runners have Apple silicon chips.
         os: [ ubuntu-latest, macos-13, windows-latest ]
-        python-version: [ 3.9, "3.10", "3.11", "3.12", "3.13"]
+        python-version: [ 3.9, "3.10", "3.11", "3.12", "3.13", "3.13t"]
         link_mkl: [true]
 
     env:
@@ -139,7 +139,7 @@ jobs:
         run: conda install -y openblas pkgconfig
 
       - name: Build wheels
-        uses: pypa/[email protected].2
+        uses: pypa/[email protected].3
 
       - uses: actions/upload-artifact@v4
         with:

pyproject.toml

@@ -23,6 +23,7 @@ dependencies = [
 [tool.cibuildwheel]
 # Load SCS source submodule, already done in CI/CD
 before-all = "git submodule update --init"
+enable = ["cpython-freethreading"]
 skip = [
   "pp*", # Disable building PyPy wheels on all platforms
   "*-win32", # fails on locating Python headers, probably meson.build is misconfigured