Godot: Script which inherits from a class defined by `class_name` keyword does not feature the parent's attributes in the inspector

[OliPerraul]

Godot version:

Related PR
https://github.com/godotengine/godot/pull/20233

Steps to reproduce:

1. Create a gdscript with global scope, using the the class_name keyword
2. Declare a an export(..) var inside the gdscript
3. Inherit from the declared class from anohter gdscript.
4. Attach the gdscript to a node in the inspector.
5. Notice the the parent node's export attributes are not featured in the inspector. (I tried restarting godot too)

[Piet-G]

This is still broken in master, I feel this is a rather big issue and would make class_name really hard to work with.