### 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)
return gui.last_mouse_pos;
}
void Viewport::warp_mouse(const Vector2 &p_position) {
	Transform2D xform = get_screen_transform();
	Vector2 gpos = xform.xform(p_position);
	Input::get_singleton()->warp_mouse(gpos);
}
void Viewport::_gui_sort_roots() {
	if (!gui.roots_order_dirty) {
		return;
	}
	gui.roots.sort_custom<Control::CComparator>();
	gui.roots_order_dirty = false;
}
void Viewport::_gui_cancel_tooltip() {
	gui.tooltip_control = nullptr;
	if (gui.tooltip_timer.is_valid()) {
		gui.tooltip_timer->release_connections();
		gui.tooltip_timer = Ref<SceneTreeTimer>();
	}
	if (gui.tooltip_popup) {
		gui.tooltip_popup->queue_free();
	}
}
String Viewport::_gui_get_tooltip(Control *p_control, const Vector2 &p_pos, Control **r_tooltip_owner) {