### 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
old_static_variables_indices = static_variables_indices;
	old_static_variables = static_variables;
	for (KeyValue<StringName, Ref<GDScript>> &inner : subclasses) {
		inner.value->_save_old_static_data();
	}
}
void GDScript::_restore_old_static_data() {
	for (KeyValue<StringName, MemberInfo> &E : old_static_variables_indices) {
		if (static_variables_indices.has(E.key)) {
			static_variables.write[static_variables_indices[E.key].index] = old_static_variables[E.value.index];
		}
	}
	old_static_variables_indices.clear();
	old_static_variables.clear();
	for (KeyValue<StringName, Ref<GDScript>> &inner : subclasses) {
		inner.value->_restore_old_static_data();
	}
}
#endif
Error GDScript::reload(bool p_keep_state) {