Tweak tox config and add dedicated Wagtail 2.15 entry

.github/workflows/test.yml

@@ -47,7 +47,7 @@ jobs:
       matrix:
         python: ['3.7', '3.8', '3.9']
         django: ['2.2', '3.0', '3.1']
-        wagtail: ['2.11', '2.12', '2.13', '2.14']
+        wagtail: ['2.11', '2.12', '2.13', '2.14', '2.15']
         postgres: ['10.8']
         experimental: [false]
         include:
@@ -59,7 +59,7 @@ jobs:
             experimental: false
           - python: '3.9'
             django: '3.2'
-            wagtail: 'git+https://github.com/wagtail/wagtail.git@main#egg=wagtail'
+            wagtail: 'main'
             experimental: true
         exclude:
           # Exclude tests of Django 2.2 and Wagtail 2.14 together

tox.ini

@@ -2,7 +2,7 @@
 skipsdist = True
 usedevelop = True
 
-envlist = python{3.7,3.8,3.9}-django{2.2,3.0,3.1,3.2,master}-wagtail{2.11,2.12,2.13,main}-{sqlite,postgres}
+envlist = python{3.7,3.8,3.9}-django{2.2,3.0,3.1,3.2,main}-wagtail{2.11,2.12,2.13,main}-{sqlite,postgres}
 
 [flake8]
 # E501: Line too long
@@ -26,13 +26,13 @@ deps =
     django3.0: Django>=3.0,<3.1
     django3.1: Django>=3.1,<3.2
     django3.2: Django>=3.2,<4.0
-    djangomaster: git+https://github.com/django/django.git@master#egg=Django
-    djangomaster: git+https://github.com/wagtail/django-modelcluster.git
+    djangomain: git+https://github.com/django/django.git@main#egg=Django
 
     wagtail2.11: wagtail>=2.11,<2.12
     wagtail2.12: wagtail>=2.12,<2.13
     wagtail2.13: wagtail>=2.13,<2.14
-    wagtail2.14: wagtail==2.14rc1
+    wagtail2.14: wagtail>=2.14,<2.15
+    wagtail2.15: wagtail>=2.15,<2.16
     wagtailmain: git+https://github.com/wagtail/wagtail.git
 
     # Pinned to work around UTC connection error