Added back #nullable enable to generated files

Author: Triogap

Generator/CodeGenerator.cs

@@ -105,6 +105,7 @@ private string GenerateClassCode(string namespaceName, string className, string
              *   Any changes made to this file will be overwritten.       *
              *                                                            *
              **************************************************************/
+            #nullable enable
             """);
         sb.AppendLine($"namespace System.Management.Types.{namespaceName};");
         sb.AppendLine();