Django 3.1 is currently in RC, so it will be out before long. To
prepare, we're adding support for 3.1.
There isn't much in the way of changes here, just a new concrete_model
key in Model._meta
that had to be set for our mock models, removal of
the legacy FieldDoesNotExist
compatibility import (this moved from
django.db.models.fields
to django.core.exceptions
in Django 1.8),
and some small changes to our tests to handle some minor SQL schema
changes (just bringing back a missing space before DESC
that's been
gone since Django 2.0).