Misleading example about casting String as int.

**Your Godot version:**
4.0.stable

**Issue description:**
Casting.

It seems that this part in the docs is wrong:

```gdscript
# For built-in types, they will be forcibly converted if possible, otherwise the engine will raise an error.

var my_int: int
my_int = "123" as int # The string can be converted to int.
```

If you try to do this right now in Godot 4.0.stable, you will get an Error.

```Cannot cast a value of type "String" as "int"```

**URL to the documentation page:**
https://docs.godotengine.org/en/stable/tutorials/scripting/gdscript/gdscript_basics.html#casting

If you know how to fix the issue you are reporting please
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writing documentation at https://docs.godotengine.org/en/stable/community/contributing/docs_writing_guidelines.html
and contributing to the class reference here: https://docs.godotengine.org/en/stable/community/contributing/updating_the_class_reference.html