### Godot version

4.0.3-stable

### System information

Windows 10

### Issue description

In some projects ViewportTexture remains pink and doesn't render viewport content after upgrading from 4.0.2-stable to 4.0.3-stable. If a pair of files viewport.h/viewport.cpp are downgraded back to what they were in 4.0.2-stable, problem goes away.

This is how it looks in 4.0.3-stable:
![4 0 3_stable_viewport_4 0 3](https://github.com/godotengine/godot/assets/1449921/44c191a9-4b67-4b02-90b6-4ab615f62a73)

And this is how it looks if viewport.h/viewport.cpp are downgraded back to what they were in 4.0.2-stable.
![4 0 3_stable_viewport_4 0 2](https://github.com/godotengine/godot/assets/1449921/f5abc605-f129-4222-9c0e-e9a07621dd9d)



### Steps to reproduce

Unfortunately, I cannot come up wit a simple demo project reproducing the problem. It exists in some projects and doesn't exist in others.


### Minimal reproduction project

Cannot produce a simple project reproducing the problem. In simple projects it works fine.
ERR_READ_THREAD_GUARD_V(Ref<World2D>());
	if (world_2d.is_valid()) {
		return world_2d;
	} else if (parent) {
		return parent->find_world_2d();
	} else {
		return Ref<World2D>();
	}
}
void Viewport::_propagate_viewport_notification(Node *p_node, int p_what) {
	p_node->notification(p_what);
	for (int i = 0; i < p_node->get_child_count(); i++) {
		Node *c = p_node->get_child(i);
		if (Object::cast_to<Viewport>(c)) {
			continue;
		}
		_propagate_viewport_notification(c, p_what);
	}
}
Ref<World2D> Viewport::get_world_2d() const {
	ERR_READ_THREAD_GUARD_V(Ref<World2D>());
	return world_2d;
}
Camera2D *Viewport::get_camera_2d() const {