[1.5.x] Fixed #19776 -- Added missing import for backport

from django.contrib.auth.tests.custom_user import ExtensionUser, CustomPermissionsUser, CustomUser

from django.contrib.contenttypes.models import ContentType

from django.core.exceptions import ImproperlyConfigured

from django.contrib.auth import authenticate

from django.test import TestCase

from django.test.utils import override_settings