chore: adds missing using

Author: baywet

test/Microsoft.OpenApi.Tests/Models/OpenApiSecuritySchemeTests.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.IO;
+using System.Text.Json.Nodes;
 using System.Threading.Tasks;
 using VerifyXunit;
 using Xunit;