install dependencies needed to create the source distribution

Author: grlee77

.github/workflows/wheel_tests_and_release.yml

@@ -187,6 +187,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install twine
+          pip install "cython<3" numpy
       
       - uses: actions/download-artifact@v2
         id: download