Fixing using statement

Author: joperezr

src/System.Device.Gpio/System/Device/Gpio/PinNumberingScheme.cs

@@ -1,7 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-namespace System;
+using System;
 namespace System.Device.Gpio;
 
 /// <summary>