Missing migration for TokenProxy in 3.12 release

[miterion]

Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

• Look at https://github.com/encode/django-rest-framework/tree/3.12.0/rest_framework/authtoken/migrations to see that there is no migration introducing the TokenProxy model.
• Alternatively (the way I found it): Have a django project which uses the rest-framework complain on startup that a migration is missing for the TokenProxy model.

Expected behavior

An existing migration for the TokenProxy model.

Actual behavior

No migration for the TokenProxy model.