Add Django 4.0 and Python 3.10 to test matrix, remove unsupported versions

Author: j4mie

.github/workflows/ci.yml

@@ -9,8 +9,15 @@ jobs:
 
     strategy:
       matrix:
-        python: [3.6, 3.7, 3.8, 3.9]
-        django: [3.1, 3.2]
+        python: [3.6, 3.7, 3.8, 3.9, "3.10"]
+        django: [2.2, 3.2, 4.0]
+        exclude:
+          - python: 3.6
+            django: 4.0
+          - python: 3.7
+            django: 4.0
+          - python: "3.10"
+            django: 2.2
         database_url:
           - postgres://runner:password@localhost/project
           - mysql://root:[email protected]/project