Fix and test data migration error from DAB RBAC

[AlanCoding]

SUMMARY

I can explain how this bug was introduced...

One of the latest things done before merging the prior PR that integrated the RBAC app from the DAB library was that the RoleDefinition names were changed to a new naming convention. As a part of this, we didn't want to use all-lowercase names like "jobtemplate", so I called model_class on the ContentType object.

Testing this with the "current" unit tests, you would just pass in the "current" apps, which would have that method. However, with historical migrations, you're using partial models that don't have such methods available.

Thus, #15137

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API

[AlanCoding]

First version had a failure with

django.db.utils.IntegrityError: NOT NULL constraint failed: main_organization.created

and that was just due to creating the organization object the test needs. I saw this failure locally, and I expect to see it in the checks here. I made a change to the test and am trying to verify that locally before pushing, but it seems these tests can take on the order of ~10 minutes.