### Godot version

v4.2.rc.mono.custom_build [ad72de508]

### System information

Windows 10

### Issue description

As I pointed out several times earlier in [#80284](https://github.com/godotengine/godot/pull/80284#issuecomment-1722120503), the references to singletons in `GDScript` are still not updated after the `GDExtension` reload.

https://github.com/godotengine/godot/assets/7782218/f90052a5-0de2-4310-8235-f0b9e2f74b3a

Singletons themselves are updated and work correctly, but references to these singletons are not updated in `@tool` scripts. That is, `Engine.get_singleton` returns the actual working reference, but using the singleton directly through its name causes errors.

### Steps to reproduce

* Clone `4.2.reload_singleton` branch from the MRP repository https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton
* Build as usual
* Open the project from the `project/` folder
* Add one character to the source code and rebuild
* Focus on the editor to reload extension
* Watch for error spam when calling by singleton name

### Minimal reproduction project

https://github.com/DmitriySalnikov/gde_test_cases/tree/4.2.reload_singleton
} else {
				for (List<Pair<StringName, Variant>>::Element *G = saved_state.front(); G; G = G->next()) {
					script_inst->set(G->get().first, G->get().second);
				}
			}
			scr->pending_reload_state.erase(obj->get_instance_id()); 
		}
		
	}
#endif
}
void GDScriptLanguage::frame() {
	calls = 0;
#ifdef DEBUG_ENABLED
	if (profiling) {
		MutexLock lock(this->mutex);
		SelfList<GDScriptFunction> *elem = function_list.first();
		while (elem) {
			elem->self()->profile.last_frame_call_count = elem->self()->profile.frame_call_count.get();
			elem->self()->profile.last_frame_self_time = elem->self()->profile.frame_self_time.get();
			elem->self()->profile.last_frame_total_time = elem->self()->profile.frame_total_time.get();
			elem->self()->profile.frame_call_count.set(0);
			elem->self()->profile.frame_self_time.set(0);
			elem->self()->profile.frame_total_time.set(0);
			elem = elem->next();
		}
	}
#endif
}
void GDScriptLanguage::get_reserved_words(List<String> *p_words) const {