### 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_MAIN_THREAD_GUARD;
	gui.canvas_sort_index = 0;
}
int Viewport::gui_get_canvas_sort_index() {
	ERR_MAIN_THREAD_GUARD_V(0);
	return gui.canvas_sort_index++;
}
void Viewport::gui_release_focus() {
	ERR_MAIN_THREAD_GUARD;
	if (gui.key_focus) {
		Control *f = gui.key_focus;
		gui.key_focus = nullptr;
		f->notification(Control::NOTIFICATION_FOCUS_EXIT, true);
		f->queue_redraw();
	}
}
Control *Viewport::gui_get_focus_owner() const {
	ERR_READ_THREAD_GUARD_V(nullptr);
	return gui.key_focus;
}
void Viewport::set_msaa_2d(MSAA p_msaa) {
	ERR_MAIN_THREAD_GUARD;
	ERR_FAIL_INDEX(p_msaa, MSAA_MAX);
	if (msaa_2d == p_msaa) {
		return;
	}
	msaa_2d = p_msaa;
	RS::get_singleton()->viewport_set_msaa_2d(viewport, RS::ViewportMSAA(p_msaa));
}
Viewport::MSAA Viewport::get_msaa_2d() const {