Skip setup-python on macOS, use system Python instead

setup-python's internal install script hardcodes /Users/runner which
fails on self-hosted runners without sudo. macOS ships with Python 3
so we use it directly and skip the action entirely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/build.yml

@@ -33,18 +33,23 @@ jobs:
       - uses: actions/checkout@v4
 
       - name: Set up Python
+        if: matrix.platform != 'macos'
         uses: actions/setup-python@v5
         with:
           python-version: ${{ env.PYTHON_VERSION }}
-        env:
-          AGENT_TOOLSDIRECTORY: ${{ runner.temp }}/toolcache
+
+      - name: Verify Python (macOS)
+        if: matrix.platform == 'macos'
+        run: |
+          python3 --version
+          python3 -m pip --version
 
       - name: Install Python build tools
-        run: python -m pip install --upgrade pip setuptools wheel
+        run: python3 -m pip install --upgrade pip setuptools wheel
 
       - name: Build sidecar
         working-directory: python
-        run: python build_sidecar.py --cpu-only
+        run: python3 build_sidecar.py --cpu-only
 
       - name: Upload sidecar artifact
         uses: actions/upload-artifact@v3