### 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)
if (o) {
			CollisionObject2D *co = Object::cast_to<CollisionObject2D>(o);
			if (co && co->is_inside_tree()) {
				if (p_clean_all_frames && p_paused_only && co->can_process()) {
					continue;
				}
				co->_mouse_shape_exit(E.key.second);
			}
		}
		shapes_to_erase.push_back(E.key);
	}
	while (shapes_to_erase.size()) {
		physics_2d_shape_mouseover.erase(shapes_to_erase.front()->get());
		shapes_to_erase.pop_front();
	}
}
void Viewport::_gui_grab_click_focus(Control *p_control) {
	gui.mouse_click_grabber = p_control;
	call_deferred(SNAME("_post_gui_grab_click_focus"));
}
void Viewport::_post_gui_grab_click_focus() {
	Control *focus_grabber = gui.mouse_click_grabber;
	if (!focus_grabber) {
		
		return;
	}
	gui.mouse_click_grabber = nullptr;
	if (gui.mouse_focus) {
		if (gui.mouse_focus == focus_grabber) {
			return;