test: adjust versions tox runs

Author: nedbat

tox.ini

@@ -14,11 +14,11 @@
 
 [tox]
 envlist =
-    py38-django{22,32,42}-cov{6,7,tip},
+    py38-django{22,32,42}-cov{6,7},
     py39-django{22,32,42}-cov{6,7,tip},
-    py310-django{32,42,tip}-cov{6,7,tip},
-    py311-django{42,tip}-cov{6,7,tip},
-    py312-django{tip}-cov{7,tip},
+    py310-django{32,42,51,tip}-cov{6,7,tip},
+    py311-django{42,51,tip}-cov{6,7,tip},
+    py312-django{51,tip}-cov{7,tip},
     check,pkgcheck,doc
 
 [testenv]
@@ -29,6 +29,7 @@ deps =
     django22: Django>=2.2,<3.0
     django32: Django>=3.2,<4.0
     django42: Django>=4.2,<5.0
+    django42: Django>=5.1,<6.0
     djangotip: git+https://github.com/django/django.git
     pytest
     unittest-mixins==1.6