chore: Add NGO_EXCLUDE_HEAVY_TESTS define (#4114)

Add NGO_EXCLUDE_HEAVY_TESTS

Author: mnachury-unity

com.unity.netcode.gameobjects/Tests/Editor/Build/BuildTests.cs

@@ -1,3 +1,4 @@
+#if !NGO_EXCLUDE_HEAVY_TESTS
 using System.IO;
 using System.Reflection;
 using NUnit.Framework;
@@ -40,3 +41,4 @@ public void BasicBuildTest()
         }
     }
 }
+#endif