Add _Notification event workacround to C# file

[GrahameGW]

As explained in https://github.com/nathanhoad/godot_dialogue_manager/issues/589, a workaround is needed because Godot calls a translation notification before the object is loaded. @nathanhoad already did it for GDScript but it doesn't seem to have made it into the C# version

[mikhail-shafigullin]

I had the same problem with sharp code.

[nathanhoad]

Oh yeah, I changed the balloon in the examples directory but forgot to change the actual example balloon.