Rename Django's dev branch to main.

More information: https://groups.google.com/g/django-developers/c/tctDuKUGosc/
Refs: django/django#14048

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
       max-parallel: 5
       matrix:
         python-version: ['3.6', '3.7', '3.8', '3.9']
-        django-version: ['2.2', '3.0', '3.1', 'dev']
+        django-version: ['2.2', '3.0', '3.1', 'main']
 
     steps:
     - uses: actions/checkout@v2

tox.ini

@@ -1,6 +1,7 @@
 [tox]
 envlist =
-    py{36,37,38}-dj{22,30,31,dev}
+    py{36,37,38,39}-dj{22,30,31}
+    py{38,39}-djmain
     qa
 
 [gh-actions]
@@ -15,18 +16,18 @@ DJANGO =
     2.2: dj22
     3.0: dj30
     3.1: dj31
-    dev: djdev
+    main: djmain
 
 [testenv]
 deps =
     coverage
     dj22: django>=2.2,<2.3
     dj30: django>=3.0,<3.1
     dj31: django>=3.1,<3.2
-    djdev: https://github.com/django/django/archive/master.tar.gz
+    djmain: https://github.com/django/django/archive/main.tar.gz
 usedevelop = True
 ignore_outcome =
-    djdev: True
+    djmain: True
 commands =
     {envbindir}/coverage run {envbindir}/django-admin test -v2 --settings=tests.settings
     {envbindir}/coverage report -m