test(analytics): add missing unit parameter in mixpanel data client test

- Include MixpanelTimeUnit.day in contentPropertiesEvent query to ensure test consistency

Author: fulleni

test/src/services/analytics/mixpanel_data_client_test.dart

@@ -141,6 +141,7 @@ void main() {
           event: 'contentViewed',
           fromDate: '2024-01-01',
           toDate: '2024-01-07',
+          unit: MixpanelTimeUnit.day,
         );
 
         verify(