Update python-package.yml

Author: orbitfold

.github/workflows/python-package.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ['3.7', '3.8']
+        python-version: ['3.7', '3.8', '3.9']
 
     steps:
     - uses: actions/checkout@v2