### 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 (over) {
			bool stopped = false;
			if (over->can_process()) {
				Transform2D localizer = over->get_global_transform_with_canvas().affine_inverse();
				Size2 pos = localizer.xform(drag_event->get_position());
				Vector2 velocity = localizer.basis_xform(drag_event->get_velocity());
				Vector2 rel = localizer.basis_xform(drag_event->get_relative());
				drag_event = drag_event->xformed_by(Transform2D()); 
				drag_event->set_velocity(velocity);
				drag_event->set_relative(rel);
				drag_event->set_position(pos);
				stopped = _gui_call_input(over, drag_event);
			}
			if (stopped) {
				set_input_as_handled();
			}
			return;
		}
	}
	if (mm.is_null() && mb.is_null() && p_event->is_action_type()) {
		if (gui.dragging && p_event->is_action_pressed("ui_cancel") && Input::get_singleton()->is_action_just_pressed("ui_cancel")) {
			_perform_drop();
			set_input_as_handled();
			return;
		}
		if (gui.key_focus && !gui.key_focus->is_visible_in_tree()) {
			gui.key_focus->release_focus();
		}
		if (gui.key_focus) {
			gui.key_event_accepted = false;