Bug fix in KerasObjectLoader.cs

I added `ToArray()` so that there is no "The collection has changed" error after `_delete_tracking`.

src/TensorFlowNET.Keras/Saving/KerasObjectLoader.cs

@@ -174,7 +174,7 @@ namespace Tensorflow.Keras.Saving
                 }
                 if(node is Functional functional)
                 {
-                    foreach(var name in functional.UnconditionalDependencyNames.Keys)
+                    foreach(var name in functional.UnconditionalDependencyNames.Keys.ToArray())
                     {
                         if(Regex.Match(name, @"^layer(_with_weights)?-[\d+]").Success)
                         {