add tests for python 3.9 and 3.10

Author: Chilipp

.github/workflows/python-app.yml

@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        python-version: [3.6, 3.7, 3.8]
+        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
         sphinx-version: ["", "4.5", "4.4", "4.3", "4.2", "4.1", "4.0.*", "3.5.*", "3.4.*", "3.2.*",  "3.1.*", "3.0.*", "2.4.*", "2.3.*", "2.2.*"]
 
     steps: