Updated Git branch "master" to "main".

This change follows a long discussion on django-develops:

https://groups.google.com/g/django-developers/c/tctDuKUGosc/

Refs django/django#14048

Author: MarkusH

trac-env/conf/trac.ini

@@ -57,7 +57,7 @@ webadmin.ticket.* = enabled
 webadmin.web_ui.* = enabled
 
 [github]
-branches = master stable/*
+branches = main stable/*
 client_id = GITHUB_OAUTH_CLIENT_ID
 client_secret = GITHUB_OAUTH_CLIENT_SECRET
 repository = django/django