Fix CI: use venv for sdist install, update macOS runners

- sdist job: use uv venv instead of --system to avoid PEP 668 error
  on macos-14 with externally managed Homebrew Python
- wheels_macos: use macos-14 for all arches (macos-13 is deprecated)
  cibuildwheel handles x86_64 cross-compilation via CIBW_ARCHS_MACOS

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mrecachinas

.github/workflows/pythonpackage.yml

@@ -60,7 +60,9 @@ jobs:
       run: uv build --sdist --out-dir wheelhouse
 
     - name: Install from sdist
-      run: uv pip install --system wheelhouse/*.tar.gz
+      run: |
+        uv venv .venv
+        uv pip install --python .venv/bin/python wheelhouse/*.tar.gz
 
     - name: Check sdist
       run: |
@@ -77,7 +79,7 @@ jobs:
     if: startsWith(github.ref, 'refs/tags')
     needs: [build-and-test, sdist]
     name: Build macOS ${{ matrix.cibw_python }} ${{ matrix.cibw_arch }} wheels
-    runs-on: ${{ matrix.cibw_arch == 'arm64' && 'macos-14' || 'macos-13' }}
+    runs-on: macos-14
     strategy:
       fail-fast: true
       matrix: