Add Python 3.10

Author: fabaff

.github/workflows/testing.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [ 3.8, 3.9 ]
+        python-version: [ "3.8", "3.9", "3.10" ]
 
     steps:
     - name: Checkout