Update AppThemeModeService.cs

Author: yaira2

src/Files.App/Services/App/AppThemeModeService.cs

@@ -5,6 +5,7 @@
 using Microsoft.UI.Windowing;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Media;
+using System.Runtime.InteropServices;
 using Windows.UI;
 using Windows.UI.ViewManagement;