Add pragma warning suppression for IWebHost obsolete warning in TransportTestHelpers

Co-authored-by: BrennanConroy <[email protected]>

Author: Copilot

src/Servers/Kestrel/shared/test/TransportTestHelpers/IWebHostPortExtensions.cs

@@ -1,6 +1,8 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+#pragma warning disable CS0618 // Type or member is obsolete
+
 using System;
 using System.Collections.Generic;
 using System.Linq;