fix(country): use Object instead of dynamic for empty list type

- Change type of 'matchingSources' and 'matchingHeadlines' from List<dynamic> to List<Object> in country query service
- This modification improves type safety and eliminates potential type-related issues

Author: fulleni

lib/src/services/country_query_service.dart

@@ -174,7 +174,7 @@ class CountryQueryService {
       });
       pipeline.add({
         r'$match': {
-          'matchingSources': {r'$ne': <dynamic>[]},
+          'matchingSources': {r'$ne': <Object>[]},
         },
       });
     }
@@ -202,7 +202,7 @@ class CountryQueryService {
       });
       pipeline.add({
         r'$match': {
-          'matchingHeadlines': {r'$ne': <dynamic>[]},
+          'matchingHeadlines': {r'$ne': <Object>[]},
         },
       });
     }