Add Django 5.0 support.

tox.ini

@@ -4,6 +4,7 @@ envlist =
     py{38,39,310}-django40
     py{38,39,310,311,312}-django41
     py{38,39,310,311,312}-django42
+    py{310,311,312}-django50
     lint
     coverage
 
@@ -27,6 +28,7 @@ deps =
     django40: django>=4.0,<4.1
     django41: django>=4.1,<4.2
     django42: django>=4.2,<4.3
+    django50: django>=5.0,<5.1
 
 [testenv:lint]
 basepython = python3.11