Support Python 3.13 and Django 5.1.

tox.ini

@@ -5,6 +5,7 @@ envlist =
     py{38,39,310,311,312}-django41
     py{38,39,310,311,312}-django42
     py{310,311,312}-django50
+    py{310,311,312,313}-django51
     lint
     coverage
 
@@ -16,6 +17,7 @@ python =
     3.10: py310
     3.11: py311
     3.12: py312
+    3.13: py313
 
 [testenv]
 allowlist_externals = ./manage.py
@@ -29,9 +31,10 @@ deps =
     django41: django>=4.1,<4.2
     django42: django>=4.2,<4.3
     django50: django>=5.0,<5.1
+    django51: django>=5.1,<5.2
 
 [testenv:lint]
-basepython = python3.11
+basepython = python3.12
 deps = pre-commit
 commands = pre-commit run --all-files --show-diff-on-failure