Add supported django versions and sqlite url to CI

Author: j4mie

.github/workflows/ci.yml

@@ -9,11 +9,12 @@ jobs:
 
     strategy:
       matrix:
-        python: [3.6, 3.7, 3.8]
-        django: [2.2]
+        python: [3.6, 3.7, 3.8, 3.9]
+        django: [3.1, 3.2rc1]
         database_url:
           - postgres://runner:password@localhost/project
           - mysql://root:[email protected]/project
+          - sqlite:///:memory:
 
     services:
       postgres: