GeneratorKind: fix bug introduced while migrating from enum to class

src/Generator/GeneratorKind.cs

@@ -104,6 +104,11 @@ namespace CppSharp.Generators
             }
         }
 
+        public override string ToString()
+        {
+            return ID;
+        }
+
         public const string CLI_ID = "CLI";
         public static readonly GeneratorKind CLI = new(CLI_ID, "C++/CLI", typeof(CLIGenerator), typeof(CLITypePrinter), new[] { "cli" });