Add Django 4.0 support on tox

Author: r-lelis

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{36,37,38,39,py}-{dj22,dj30,dj31,dj32}-{fl10,fl11,fl20}
+    py{36,37,38,39,py}-{dj22,dj30,dj31,dj32}-{fl10,fl11,fl20},py{38,39,py}-{dj40}
 
 [testenv]
 basepython =
@@ -23,6 +23,8 @@ deps =
     dj30: Django>=3.0,<3.1
     dj31: Django>=3.1,<3.2
     dj32: Django>=3.2,<3.3
+    dj40: Django>=4.0,<4.1
+
 commands =
     pytest --cov=restless
 
@@ -40,6 +42,8 @@ DJANGO =
     3.0: dj30
     3.1: dj31
     3.2: dj32
+    4.0: dj40
+
 FLASK =
     1.0: fl10
     1.1: fl11