Update AttachedCardShadow.cs

Fix DependencyProperty registration

Author: chris-blackman

Microsoft.Toolkit.Uwp.UI.Media/Shadows/AttachedCardShadow.cs

@@ -56,7 +56,7 @@ public sealed class AttachedCardShadow : AttachedShadowBase
             DependencyProperty.Register(
                 nameof(InnerContentClipMode),
                 typeof(InnerContentClipMode),
-                typeof(AttachedCardShadowBase),
+                typeof(AttachedCardShadow),
                 new PropertyMetadata(InnerContentClipMode.CompositionGeometricClip, OnDependencyPropertyChanged));
 
         /// <summary>