ci: build CPython 3.14 wheels (bump cibuildwheel to 4.x)

.github/workflows/python-package.yml

@@ -203,7 +203,10 @@ jobs:
         with:
           fetch-depth: 0
       - name: Build wheels
-        uses: pypa/cibuildwheel@v2.21.3
+        # cibuildwheel 2.21.3 predates CPython 3.14, so `build = "cp3*"`
+        # stopped at cp313 and no 3.14 wheels were published (issue #715).
+        # 4.x builds 3.14 by default and still supports cp310-cp313.
+        uses: pypa/cibuildwheel@v4.1.0
       - uses: actions/upload-artifact@v4
         with:
           name: cibw-wheels-${{ matrix.os }}

pyproject.toml

@@ -117,7 +117,12 @@ testpaths = [
 build = "cp3*"
 
 archs = ["auto64"]
-skip = ["*musllinux*"]
+# Skip musllinux, and skip the free-threaded builds (cp313t/cp314t): as of
+# cibuildwheel 3.1 free-threading is no longer experimental for 3.14, so
+# `cp3*` would otherwise build free-threaded wheels for the Cython extension,
+# which has not been validated under a no-GIL interpreter.  Drop `cp31?t-*`
+# from this list once faust is verified free-threading-safe.
+skip = ["*musllinux*", "cp31?t-*"]
 
 before-build = "pip install Cython"