### 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)
CodeEdit *text_edit = code_editor->get_text_editor();
	Node *base = get_tree()->get_edited_scene_root();
	if (base) {
		base = _find_node_for_script(base, base, script);
	}
	ScriptLanguage::LookupResult result;
	String lc_text = code_editor->get_text_editor()->get_text_for_symbol_lookup();
	Error lc_error = script->get_language()->lookup_code(lc_text, p_symbol, script->get_path(), base, result);
	bool is_singleton = ProjectSettings::get_singleton()->has_autoload(p_symbol) && ProjectSettings::get_singleton()->get_autoload(p_symbol).is_singleton;
	if (lc_error == OK || is_singleton || ScriptServer::is_global_class(p_symbol) || p_symbol.is_resource_file() || p_symbol.begins_with("uid://")) {
		text_edit->set_symbol_lookup_word_as_valid(true);
	} else if (p_symbol.is_relative_path()) {
		String path = _get_absolute_path(p_symbol);
		if (FileAccess::exists(path)) {
			text_edit->set_symbol_lookup_word_as_valid(true);
		} else {
			text_edit->set_symbol_lookup_word_as_valid(false);
		}
	} else {
		text_edit->set_symbol_lookup_word_as_valid(false);
	}
}
String ScriptTextEditor::_get_absolute_path(const String &rel_path) {