Update ArtifactExtensionsTests.cs

Author: chenzhitong

tests/Neo.SmartContract.Testing.UnitTests/Extensions/ArtifactExtensionsTests.cs

@@ -20,6 +20,7 @@ public void TestGetArtifactsSource()
 
             Assert.AreEqual(source, """
                                     using Neo.Cryptography.ECC;
+                                    using Neo.Extensions;
                                     using System;
                                     using System.Collections.Generic;
                                     using System.ComponentModel;