Added testing on Django 5.1

tox.ini

@@ -6,7 +6,8 @@ envlist =
     {py38,py39,py310,py311,pypy39}-django-4.1
     {py38,py39,py310,py311,pypy39}-django-4.2
     {py310,py311,py312}-django-5.0
-    {py310,py311,py312}-django-main
+    {py310,py311,py312,py313}-django-5.1
+    {py310,py311,py312,py313}-django-main
 
 [testenv]
 basepython =
@@ -15,6 +16,7 @@ basepython =
     py310: python3.10
     py311: python3.11
     py312: python3.12
+    py313: python3.13
     pypy39: pypy3.9
 usedevelop = true
 pip_pre = true
@@ -26,15 +28,16 @@ deps =
     django-3.2: Django>=3.2,<3.3
     django-4.1: Django>=4.1,<4.2
     django-4.2: Django>=4.2,<4.3
-    django-5.0: Django>=5.0rc1,<5.1
+    django-5.0: Django>=5.0,<5.1
+    django-5.1: Django>=5.1,<5.2
     django-main: https://github.com/django/django/archive/main.tar.gz
     -r{toxinidir}/tests/requirements.txt
 
 [testenv:docs]
 deps =
     Sphinx>=1.3
     -r{toxinidir}/docs/requirements.txt
-basepython = python3.11
+basepython = python3.12
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees docs docs/_build/html