PyPI CD: forgot the actual build!

Author: Robert Sachunsky

.github/workflows/pypi.yml

@@ -27,5 +27,6 @@ jobs:
         TWINE_USERNAME: __token__
         TWINE_PASSWORD: ${{ secrets.PYPI_TOKEN }}
       run: |
+        python -m build .
         ls -l dist
         twine upload --verbose dist/ocrd*{tar.gz,whl}