fix(default-user-preference-limit): change log level for saved headline filters limit

- Change log level from 'severe' to 'warning' when user exceeds the total saved headline filter limit
- This modification provides a less critical log level for this specific scenario while still alerting administrators

Author: fulleni

lib/src/services/default_user_preference_limit_service.dart

@@ -95,7 +95,7 @@ class DefaultUserPreferenceLimitService implements UserPreferenceLimitService {
     // Validate the total number of saved headline filters.
     if (updatedPreferences.savedHeadlineFilters.length >
         savedHeadlineFiltersLimit.total) {
-      _log.severe(
+      _log.warning(
         'User ${user.id} exceeded total saved headline filter limit: '
         '${savedHeadlineFiltersLimit.total} (attempted '
         '${updatedPreferences.savedHeadlineFilters.length}).',