Support Py3.11 and Django 4.1, and drop Django 2.1 support.

tox.ini

@@ -1,8 +1,8 @@
 [tox]
 envlist =
-    py{37,38,39}-django22
     py{37,38,39,310}-django32
     py{38,39,310}-django40
+    py{38,39,310,311}-django41
     lint
     coverage
 
@@ -12,6 +12,7 @@ python =
     3.8: py38
     3.9: py39
     3.10: py310
+    3.11: py311
 
 [testenv]
 commands = ./manage.py test --no-input {posargs}
@@ -21,6 +22,7 @@ deps =
     django22: django>=2.2,<2.3
     django32: django>=3.2,<3.3
     django40: django>=4.0,<4.1
+    django41: django>=4.1,<4.2
 
 [testenv:lint]
 basepython = python3.8