[PowerToys Run] Plugins StyleCop and warnings fix (#12623)

src/modules/launcher/Plugins/Community.PowerToys.Run.Plugin.UnitConverter/UnitHandler.cs

@@ -1,4 +1,8 @@
-using System;
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;