### 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
if (p_name == GDScriptLanguage::get_singleton()->strings._script_source) {
		r_ret = get_source_code();
		return true;
	}
	const GDScript *top = this;
	while (top) {
		{
			HashMap<StringName, Variant>::ConstIterator E = top->constants.find(p_name);
			if (E) {
				r_ret = E->value;
				return true;
			}
		}
		{
			HashMap<StringName, MemberInfo>::ConstIterator E = top->static_variables_indices.find(p_name);
			if (E) {
				if (E->value.getter) {
					Callable::CallError ce;