Updated Git branch "master" to "main".

[MarkusH]

This change follows a long discussion on django-develops [1].

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

Refs django/django#14048

[manfre]

Thank you for taking this on

[adamchainz]

I noticed there's this ticket version selector too, maybe in the DB?

[MarkusH]

Thanks Adam. That's not going to be a simple change. Unless we do a UPDATE t SET version = 'main' WHERE version = 'master' directly in PostgreSQL.

[adamchainz]

Presumably we can change what is visible in the drop down since someone adds the new versions of Django as they come out? Also that query doesn't look so bad..

[felixxm]

I've changed master to dev.

[MarkusH]

Thanks @felixxm !