### 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.subwindow_drag != SUB_WINDOW_DRAG_DISABLED) {
		ERR_FAIL_COND_V(gui.subwindow_focused == nullptr, false);
		Ref<InputEventMouseButton> mb = p_event;
		if (mb.is_valid() && !mb->is_pressed() && mb->get_button_index() == MouseButton::LEFT) {
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_CLOSE) {
				if (gui.subwindow_drag_close_rect.has_point(mb->get_position())) {
					
					gui.subwindow_focused->_event_callback(DisplayServer::WINDOW_EVENT_CLOSE_REQUEST);
				}
			}
			gui.subwindow_drag = SUB_WINDOW_DRAG_DISABLED;
			if (gui.subwindow_focused != nullptr) { 
				_sub_window_update(gui.subwindow_focused);
			}
		}
		Ref<InputEventMouseMotion> mm = p_event;
		if (mm.is_valid()) {
			if (gui.subwindow_drag == SUB_WINDOW_DRAG_MOVE) {
				Vector2 diff = mm->get_position() - gui.subwindow_drag_from;
				Rect2i new_rect(gui.subwindow_drag_pos + diff, gui.subwindow_focused->get_size());
				if (gui.subwindow_focused->is_clamped_to_embedder()) {
					Size2i limit = get_visible_rect().size;