### Godot version

4.1.3

### System information

Linux

### Issue description

I'm trying to make an editor plugin on Rust:

```rust
#[derive(GodotClass)]
#[class(tool, editor_plugin, init, base=EditorPlugin)]
pub struct MyEditorPluginBase {}
```

But due to some limitations, I still have to use GDScript for some specific things.

So I tried to make a subclass of this Rust class:

```gdscript
@tool
class_name MyEditorPlugin
extends MyEditorPluginBase
```

This would work if `MyEditorPluginBase` was a GDScript class, but since it's a GDExtension class in my case, it doesn't work:

> Unable to load addon script from path: 'res://addons/my_addon/my_editor_plugin.gd' Base type is not EditorPlugin.

But it obviously **IS** EditorPlugin!

![godot-editorplugin-docs](https://github.com/godotengine/godot/assets/3236464/4665deeb-30f0-45cd-bfff-56101b9d4875)

![godot-editorplugin](https://github.com/godotengine/godot/assets/3236464/b1b6ecb4-de22-4abd-91a3-e180691f67ee)

If I understand correctly, this behavior is caused by this function, which checks some mysterious "instance base type" instead of real inheritance:

https://github.com/godotengine/godot/blob/fa4a65387ea41506ecc519fc61a06da110dce51c/editor/editor_node.cpp#L3456-L3458

https://github.com/godotengine/godot/blob/fa4a65387ea41506ecc519fc61a06da110dce51c/modules/gdscript/gdscript.cpp#L260-L263

Since the [documentation](https://docs.godotengine.org/en/stable/tutorials/plugins/editor/making_plugins.html#the-script-file) doesn't say that the script must be a **direct** subclass of EditorPlugin (and an indirect subclass works fine in GDScript), I interpret this behavior as a Godot bug.

### Steps to reproduce

See above

### Minimal reproduction project

[gdext_editor_plugin_test.zip](https://github.com/godotengine/godot/files/13451014/gdext_editor_plugin_test.zip)
for (int i = 0; i < saver_count; ++i) {
		if (saver[i]->get_script_instance() && saver[i]->get_script_instance()->get_script()->get_path() == path) {
			return saver[i];
		}
	}
	return Ref<ResourceFormatSaver>();
}
bool ResourceSaver::add_custom_resource_format_saver(String script_path) {
	if (_find_custom_resource_format_saver(script_path).is_valid()) {
		return false;
	}
	Ref<Resource> res = ResourceLoader::load(script_path);
	ERR_FAIL_COND_V(res.is_null(), false);
	ERR_FAIL_COND_V(!res->is_class("Script"), false);
	Ref<Script> s = res;
	StringName ibt = s->get_instance_base_type();
	bool valid_type = ClassDB::is_parent_class(ibt, "ResourceFormatSaver");
	ERR_FAIL_COND_V_MSG(!valid_type, false, "Script does not inherit a CustomResourceSaver: " + script_path + ".");
	Object *obj = ClassDB::instantiate(ibt);
	ERR_FAIL_NULL_V_MSG(obj, false, "Cannot instance script as custom resource saver, expected 'ResourceFormatSaver' inheritance, got: " + String(ibt) + ".");
	Ref<ResourceFormatSaver> crl = Object::cast_to<ResourceFormatSaver>(obj);
	crl->set_script(s);
	ResourceSaver::add_resource_format_saver(crl);
	return true;
}
void ResourceSaver::add_custom_savers() {