Start upgrading to .NET 7

TestWindow/Properties/AssemblyInfo.cs

@@ -2,6 +2,7 @@
 using System.Resources;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Versioning;
 using System.Windows;
 
 // General Information about an assembly is controlled through the following 
@@ -16,6 +17,9 @@ using System.Windows;
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
 
+[assembly: SupportedOSPlatform("windows7.0")]
+[assembly: NeutralResourcesLanguage("en-US")]
+
 // Setting ComVisible to false makes the types in this assembly not visible 
 // to COM components.  If you need to access a type in this assembly from 
 // COM, set the ComVisible attribute to true on that type.