Code Quality: Set IsUpdateAvailable on UI thread for update services

Updated AppUpdateSideloadService and AppUpdateStoreService to set IsUpdateAvailable using DispatcherQueue. This ensures the property is updated on the UI thread, preventing potential threading issues.

Author: yaira2

src/Files.App/Services/App/AppUpdateSideloadService.cs

@@ -205,7 +205,10 @@ private async Task StartBackgroundDownloadAsync()
 
 				Logger?.LogInformation($"Download time taken: {timespan.Hours:00}:{timespan.Minutes:00}:{timespan.Seconds:00}");
 
-				IsUpdateAvailable = true;
+				MainWindow.Instance.DispatcherQueue.TryEnqueue(() =>
+				{
+					IsUpdateAvailable = true;
+				});
 			}
 			catch (IOException ex)
 			{

src/Files.App/Services/App/AppUpdateStoreService.cs

@@ -102,7 +102,11 @@ public async Task CheckForUpdatesAsync()
 			if (_updatePackages is not null && _updatePackages.Count > 0)
 			{
 				App.Logger.LogInformation("STORE: Update found.");
-				IsUpdateAvailable = true;
+
+				MainWindow.Instance.DispatcherQueue.TryEnqueue(() =>
+				{
+					IsUpdateAvailable = true;
+				});
 			}
 		}