Rename Django's dev branch to main.

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

tox.ini

@@ -4,7 +4,8 @@ envlist =
     black
     flake8
     isort
-    py{36,37,38,39}-dj{22,30,31,master}
+    py{36,37,38,39}-dj{22,30,31}
+    py{38,39}-djmain
     docs
 
 [gh-actions]
@@ -20,16 +21,16 @@ deps =
     dj22: Django>=2.2,<3.0
     dj30: Django>=3.0,<3.1
     dj31: Django>=3.1,<3.2
-    djmaster: https://github.com/django/django/archive/master.tar.gz#egg=django
+    djmain: https://github.com/django/django/archive/main.tar.gz
     coverage
 commands =
     coverage run -m django test --settings=tests.settings {posargs}
     coverage report
     coverage xml
-
-[testenv:py{36,37,38,39,py3}-dj{master}]
-ignore_errors = true
-ignore_outcome = true
+ignore_outcome =
+    djmain: True
+ignore_errors =
+    djmain: True
 
 [testenv:black]
 basepython = python3