Add test PyPI to workflow

.github/workflows/pypi.yml

@@ -63,6 +63,28 @@ jobs:
         with:
           name: cibw-sdist
           path: dist/*.tar.gz
+  upload_pypi_test:
+    needs: [build_wheels, build_sdist]
+    runs-on: ubuntu-latest
+    environment:
+      name: testpypi
+      url: https://test.pypi.org/p/cpnest
+      # upload to PyPI on every tag starting with 'v'
+      if: github.event_name == 'push' && startsWith(github.event.ref, 'refs/tags/v')
+      # alternatively, to publish when a GitHub Release is created, use the following rule:
+      #if: github.event_name == 'release' && github.event.action == 'published'
+    steps:
+      - name: Download artifacts
+        uses: actions/download-artifact@v4
+        with:
+          # unpacks all CIBW artifacts into dist/
+          pattern: cibw-*
+          path: dist
+          merge-multiple: true
+      - name: Upload release to PyPI Test
+        uses: pypa/gh-action-pypi-publish@release/v1
+        with:
+          repository-url: https://test.pypi.org/legacy/
 
   upload_pypi:
     needs: [build_wheels, build_sdist]