### 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 (p_control) {
		gui.drag_successful = _gui_drop(p_control, p_pos, false);
	} else {
		gui.drag_successful = false;
	}
	Control *drag_preview = _gui_get_drag_preview();
	if (drag_preview) {
		memdelete(drag_preview);
		gui.drag_preview_id = ObjectID();
	}
	gui.drag_data = Variant();
	gui.dragging = false;
	gui.drag_mouse_over = nullptr;
	_propagate_viewport_notification(this, NOTIFICATION_DRAG_END);
	get_base_window()->update_mouse_cursor_shape();
}
void Viewport::_gui_cleanup_internal_state(Ref<InputEvent> p_event) {