fix: Saving a loaded model

Author: GaijinOtohp

src/TensorFlowNET.Keras/Engine/Layer.Serialize.cs

@@ -27,6 +27,6 @@ public override IDictionary<string, Trackable> _trackable_children(SaveType save
             children = new Dictionary<string, Trackable>();
         }
 
-        return children.Concat(base._trackable_children(save_type, cache)).ToDictionary(x => x.Key, x => x.Value);
+        return children.Concat(base._trackable_children(save_type, cache)).GroupBy(x => x.Key).Select(g => g.First()).ToDictionary(x => x.Key, x => x.Value);
     }
 }