Add wagtail 6.3 and Django 5.1 to the test matrix

tox.ini

@@ -3,8 +3,9 @@ skipsdist = True
 usedevelop = True
 
 envlist =
-    python{3.9,3.10,3.11}-django4.2-wagtail{5.2,6.0,6.1,6.2}
-    python{3.10,3.11,3.12}-django5.0-wagtail{5.2,6.0,6.1,6.2}
+    python{3.9,3.10,3.11}-django4.2-wagtail{5.2,6.0,6.1,6.2,6.3}
+    python{3.10,3.11,3.12}-django5.0-wagtail{5.2,6.0,6.1,6.2,6.3}
+    python{3.10,3.11,3.12}-django5.1-wagtail{6.3}
     flake8
 
 [flake8]
@@ -34,12 +35,14 @@ deps =
 
     django4.2: Django>=4.2,<4.3
     django5.0: Django>=5.0,<5.1
+    django5.1: Django>=5.1,<5.2
     djangomain: git+https://github.com/django/django.git@main#egg=Django
 
     wagtail5.2: wagtail>=5.2,<5.3
     wagtail6.0: wagtail>=6.0,<6.1
     wagtail6.1: wagtail>=6.1,<6.2
     wagtail6.2: wagtail>=6.2,<6.3
+    wagtail6.3: wagtail>=6.3,<6.4
     wagtailmain: git+https://github.com/wagtail/wagtail.git
 
     postgres: psycopg2>=2.6