Add Wagtail 6.0 to test matrix

tox.ini

@@ -3,15 +3,15 @@ skipsdist = True
 usedevelop = True
 
 envlist =
-    python{3.8,3.9,3.10}-django{3.2,4.1,4.2}-wagtail{5.0,5.1,main}
-    python3.11-django4.2-wagtail{5.0,5.1,main}
+    python{3.8,3.9,3.10}-django{3.2,4.1,4.2}-wagtail{5.0,5.1}
+    python3.11-django{4.2,5.0}-wagtail{5.0,5.1,6.0,main}
 
 [gh]
 python =
     3.8 = python3.8-django{3.2,4.1,4.2}-wagtail{5.0,5.1}
-    3.9 = python3.9-django{3.2,4.1,4.2}-wagtail{5.1,main}
+    3.9 = python3.9-django{3.2,4.1,4.2}-wagtail{5.1}
     3.10 = python3.10-django{3.2,4.1,4.2}-wagtail{5.1}
-    3.11 = python3.11-django{4.1,4.2}-wagtail{main}
+    3.11 = python3.11-django{4.2,5.0}-wagtail{6.0,main}
 
 [testenv]
 install_command = pip install -e ".[testing]" -U {opts} {packages}
@@ -29,10 +29,12 @@ deps =
     django3.2: Django>=3.2,<4.0
     django4.1: Django>=4.1,<4.2
     django4.2: Django>=4.2,<4.3
+    django5.0: Django>=5.0,<5.1
     djangomain: git+https://github.com/django/django.git@main#egg=Django
 
     wagtail5.0: wagtail>=5.0,<5.1
-    wagtail5.1: git+https://github.com/wagtail/wagtail.git@stable/5.1.x#egg=wagtail
+    wagtail5.1: wagtail>=5.1,<5.2
+    wagtail6.0: git+https://github.com/wagtail/wagtail.git@stable/6.0.x#egg=wagtail
     wagtailmain: git+https://github.com/wagtail/wagtail.git#egg=wagtail
 
     postgres: psycopg2>=2.6