Add license info.

Author: irvinesunday

test/Microsoft.OpenApi.Tests/Services/OpenApiUrlSpaceTests.cs

@@ -1,4 +1,7 @@
-using System.Collections.Generic;
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license.
+
+using System.Collections.Generic;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Services;
 using Xunit;