CI: Set up CI for the free-threaded build of 3.13

Author: lysnikolaou

.github/workflows/unit-tests.yml

@@ -347,6 +347,55 @@ jobs:
       - name: Run Tests
         uses: ./.github/actions/run-tests
 
+  python-freethreading:
+    defaults:
+      run:
+        shell: bash -eou pipefail {0}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        # Separate out macOS 13 and 14, since macOS 14 is arm64 only
+        os: [ubuntu-22.04, macOS-13, macOS-14]
+
+    timeout-minutes: 90
+
+    concurrency:
+      # https://github.community/t/concurrecy-not-work-for-push/183068/7
+      group: ${{ github.event_name == 'push' && github.run_number || github.ref }}-${{ matrix.os }}-${{ matrix.pytest_target }}-dev
+      cancel-in-progress: true
+
+    env:
+      PYTEST_WORKERS: "auto"
+      PANDAS_CI: 1
+      PATTERN: "not slow and not network and not clipboard and not single_cpu"
+      PYTEST_TARGET: pandas
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Python Free-threading Version
+        uses: deadsnakes/[email protected]
+        with:
+          python-version: 3.13-dev
+          nogil: true
+
+      - name: Build Environment
+        run: |
+          python --version
+          python -m pip install --upgrade --pre pip
+          python -m pip install --upgrade setuptools wheel meson[ninja]==1.2.1 meson-python==0.13.1
+          python -m pip install --pre --extra-index-url https://pypi.anaconda.org/scientific-python-nightly-wheels/simple numpy cython
+          python -m pip install versioneer[toml]
+          python -m pip install python-dateutil pytz tzdata hypothesis>=6.46.1 pytest>=7.3.2 pytest-xdist>=2.2.0 pytest-cov
+          python -m pip install -ve . --no-build-isolation --no-index --no-deps --config-settings=setup-args="--werror"
+          python -m pip list
+
+      - name: Run Tests
+        uses: ./.github/actions/run-tests
+
   emscripten:
     # Note: the Python version, Emscripten toolchain version are determined
     # by the Pyodide version. The appropriate versions can be found in the