### 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 (gui.key_focus->can_process()) {
				gui.key_focus->_call_gui_input(p_event);
			}
			if (gui.key_event_accepted) {
				set_input_as_handled();
				return;
			}
		}
		Control *from = gui.key_focus ? gui.key_focus : nullptr;
		if (from && p_event->is_pressed()) {
			Control *next = nullptr;
			Ref<InputEventJoypadMotion> joypadmotion_event = p_event;
			if (joypadmotion_event.is_valid()) {
				Input *input = Input::get_singleton();
				if (p_event->is_action_pressed("ui_focus_next") && input->is_action_just_pressed("ui_focus_next")) {
					next = from->find_next_valid_focus();
				}
				if (p_event->is_action_pressed("ui_focus_prev") && input->is_action_just_pressed("ui_focus_prev")) {
					next = from->find_prev_valid_focus();
				}
				if (p_event->is_action_pressed("ui_up") && input->is_action_just_pressed("ui_up")) {
					next = from->_get_focus_neighbor(SIDE_TOP);
				}
				if (p_event->is_action_pressed("ui_left") && input->is_action_just_pressed("ui_left")) {
					next = from->_get_focus_neighbor(SIDE_LEFT);
				}
				if (p_event->is_action_pressed("ui_right") && input->is_action_just_pressed("ui_right")) {
					next = from->_get_focus_neighbor(SIDE_RIGHT);
				}
				if (p_event->is_action_pressed("ui_down") && input->is_action_just_pressed("ui_down")) {