Enhancement description the `get` for Array

[shinspiegel]

Your Godot version: 4.4.1

Issue description: Sightly update on the description of get method for Array

URL to the documentation page (if already existing): https://docs.godotengine.org/en/stable/classes/class_array.html#class-array-method-get

There is no mention that an out-of-bounds or invalid index will return a null value. Maybe we could append this. If so, may I do this change on the docs to also include it?