Note: this can now be done in usync with no custom code : https://github.com/KevinJump/uSync/releases/tag/8.4.4

settingsDictionaryHandler.cs

/// ****************************************************
/// NOTE: As of uSync 8.8.4 this functionaliy exists in the core of the package 
/// https://github.com/KevinJump/uSync/releases/tag/8.4.4
///
/// With ContentEdition Installed you can move the dictionayHandler with a Group="Settings" attribute in the config file.
/// ****************************************************
    
    
/// uSync Dictionary Handler 
/// untested code - in theory this would make a dictionary handler that synced with the settings group in uSync not the content one.
/// you would need to update your usync8.config. 
    
using Umbraco.Core.Cache;
using Umbraco.Core.Logging;
using Umbraco.Core.Models;
using Umbraco.Core.Services;

using uSync8.BackOffice;
using uSync8.BackOffice.Services;
using uSync8.BackOffice.SyncHandlers;
using uSync8.ContentEdition.Handlers;
using uSync8.Core;
using uSync8.Core.Dependency;
using uSync8.Core.Serialization;
using uSync8.Core.Tracking;

using static Umbraco.Core.Constants;

namespace CustomeHandlers
{
    [SyncHandler("settingsDictionaryHandler", "Dictionary", "Dictionary", uSyncBackOfficeConstants.Priorites.DictionaryItems
            , Icon = "icon-book-alt usync-addon-icon", EntityType = UdiEntityType.DictionaryItem)]
    public class SettingsDictionary : DictionaryHandler
    {
        public SettingsDictionary(ILocalizationService localizationService, IEntityService entityService, IProfilingLogger logger, AppCaches appCaches, ISyncSerializer<IDictionaryItem> serializer, ISyncItemFactory syncItemFactory, SyncFileService syncFileService) 
            : base(localizationService, entityService, logger, appCaches, serializer, syncItemFactory, syncFileService)
        { }

        protected SettingsDictionary(IEntityService entityService, IProfilingLogger logger, ILocalizationService localizationService, ISyncSerializer<IDictionaryItem> serializer, ISyncTracker<IDictionaryItem> tracker, AppCaches appCaches, ISyncDependencyChecker<IDictionaryItem> checker, SyncFileService syncFileService)
            : base(entityService, logger, localizationService, serializer, tracker, appCaches, checker, syncFileService)
        { }

        public override string Group => uSyncBackOfficeConstants.Groups.Settings;
    }
}