Django 4 requires at least Python 3.8

Author: PeterJCLaw

.circleci/config.yml

@@ -36,6 +36,11 @@ references:
       parameters:
         python-version: ["3.6", "3.7", "3.8", "3.9"]
         django-version: ["2.2", "3.0", "3.1", "3.2", "4.0"]
+      exclude:
+        - python-version: "3.6"
+          django-version: "4.0"
+        - python-version: "3.7"
+          django-version: "4.0"
 
 executors:
   python: