tests: do not run dataviz job in cron tests

tests/test_cron.py

@@ -2,11 +2,13 @@ import mock
 import pytest
 from django.core.management import call_command
 from django.core.management.base import CommandError
+from django.test import override_settings
 from django.utils.six import StringIO
 
 pytestmark = pytest.mark.django_db
 
 
+@override_settings(STATISTICS_PROVIDERS=[])
 def test_cron_run(app):
     with mock.patch('combo.apps.lingo.AppConfig.hourly') as hourly_job:
         call_command('cron')