### 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)
_gui_sort_roots();
	for (List<Control *>::Element *E = gui.roots.back(); E; E = E->prev()) {
		Control *sw = E->get();
		if (!sw->is_visible_in_tree()) {
			continue;
		}
		Transform2D xform;
		CanvasItem *pci = sw->get_parent_item();
		if (pci) {
			xform = pci->get_global_transform_with_canvas();
		} else {
			xform = sw->get_canvas_transform();
		}
		Control *ret = _gui_find_control_at_pos(sw, p_global, xform);
		if (ret) {
			return ret;
		}
	}
	return nullptr;
}
Control *Viewport::_gui_find_control_at_pos(CanvasItem *p_node, const Point2 &p_global, const Transform2D &p_xform) {