### Godot version

v4.0.beta.custom_build [0a9e6e478]

### System information

Ubuntu, Nvidia, Vulkan

### Issue description

When a Camera2D is freed - either explicitly or by being a child of a scene that is being switched away from via a method like `get_tree().change_scene_to_file()` - then this camera somehow stays active instead of Godot properly switching to no-camera-mode.

`get_viewport().get_camera_2d()` then returns all sorts of funny things from `<Freed Object>`  (it's supposed to return `null`) to arbitrary nodes of the current scene (not cameras).

This can lead to crashes.

### Steps to reproduce

checkout the MRP.

note that the "Go to scene 2" button switches places after pressing it.
that is because a camera is still active that does not exist in the current tree.

restart it a couple of times and spam the "Go to scene 2" button.
notice the garbage output.

### Minimal reproduction project

[godot_4_camera_bug.zip](https://github.com/godotengine/godot/files/10560455/godot_4_camera_bug.zip)
} else {
		vr = window->get_usable_parent_rect();
	}
	if (r.size.x + r.position.x > vr.size.x + vr.position.x) {
		
		r.position.x = gui.tooltip_pos.x - r.size.x - tooltip_offset.x;
		if (r.position.x < vr.position.x) {
			r.position.x = vr.position.x + vr.size.x - r.size.x;
		}
	} else if (r.position.x < vr.position.x) {
		r.position.x = vr.position.x;
	}
	if (r.size.y + r.position.y > vr.size.y + vr.position.y) {
		
		r.position.y = gui.tooltip_pos.y - r.size.y - tooltip_offset.y;
		if (r.position.y < vr.position.y) {
			r.position.y = vr.position.y + vr.size.y - r.size.y;
		}
	} else if (r.position.y < vr.position.y) {
		r.position.y = vr.position.y;
	}
	gui.tooltip_popup->set_position(r.position);
	gui.tooltip_popup->set_size(r.size);
	DisplayServer::WindowID active_popup = DisplayServer::get_singleton()->window_get_active_popup();
	if (active_popup == DisplayServer::INVALID_WINDOW_ID || active_popup == window->get_window_id()) {
		gui.tooltip_popup->show();
	}
	gui.tooltip_popup->child_controls_changed();
}
bool Viewport::_gui_call_input(Control *p_control, const Ref<InputEvent> &p_input) {