test: Update tests to the new return code.

When including `JwtAuthentication`, the auth_header becomes `JWT
realm="api"`. Without it, it is `None`. This changes the behavior of the
code in DRF and returns a slightly different auth response.

Relevant Code: 56946fac8f/rest_framework/views.py (L456C3-L456C3)

openedx/core/lib/api/test_utils.py

@@ -64,6 +64,10 @@ class ApiTestCase(TestCase):
         """Assert that the given response has the status code 201"""
         assert response.status_code == 201
 
+    def assertHttpNotAuthorized(self, response):
+        """Assert that the given response has the status code 401"""
+        assert response.status_code == 401
+
     def assertHttpForbidden(self, response):
         """Assert that the given response has the status code 403"""
         assert response.status_code == 403