Fix tests

Author: barseghyanartur

src/django_elasticsearch_dsl_drf/tests/test_utils.py

@@ -52,7 +52,7 @@ def _list_results(self):
 
         # Should contain no results
         self.assertEqual(response.data['results'], [])
-        self.assertEqual(response.data['count'], None)
+        self.assertEqual(response.data['count'], 0)
         self.assertEqual(response.data['next'], None)
         self.assertEqual(response.data['previous'], None)