restore release check for pypi upload

Author: fgregg

.github/workflows/build_and_upload.yml

@@ -51,6 +51,7 @@ jobs:
   upload_to_pypi:
     name: "Upload to PyPI"
     runs-on: ubuntu-latest
+    if: github.event_name == 'release' && github.event.action == 'published'
     needs:
       - build_wheels
       - make_sdist