Rename Django's dev branch to main.

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

Author: jezdez

tox.ini

@@ -16,7 +16,7 @@ deps =
     sqlite: mock
     postgresql: psycopg2-binary
     mysql: mysqlclient
-    djmain: https://github.com/django/django/archive/master.tar.gz
+    djmain: https://github.com/django/django/archive/main.tar.gz
     coverage
     Jinja2
     html5lib