Updated new file headers

Author: jamesmcroft

Microsoft.Toolkit.Uwp.UI.Controls/Expander/ExpanderAutomationPeer.cs

@@ -1,4 +1,8 @@
-using Windows.UI.Xaml.Automation;
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using Windows.UI.Xaml.Automation;
 using Windows.UI.Xaml.Automation.Peers;
 using Windows.UI.Xaml.Automation.Provider;