Update test matrix for Django 4 and Python 3.10

Author: mixxorz

tox.ini

@@ -4,23 +4,23 @@ envlist =
     flake8
     black
     isort
-    py36-django{22,31,32}
-    py37-django{22,31,32}
-    py38-django{22,31,32}
-    py39-django{22,31,32}
+    py37-django{22,32,40}
+    py38-django{22,32,40}
+    py39-django{22,32,40}
+    py310-django{22,32,40}
 
 [gh-actions]
 python =
-    3.6: py36
     3.7: py37
     3.8: py38
     3.9: py39, flake8, black, isort
+    3.10: py310, flake8, black, isort
 
 [testenv]
 deps =
     django22: Django>=2.2,<2.3
-    django31: Django>=3.1,<3.2
     django32: Django>=3.2,<3.3
+    django40: Django>=4.0,<4.1
 commands =
     python runtests.py