### 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)
return false;
}
Ref<Image> ViewportTexture::get_image() const {
	ERR_FAIL_COND_V_MSG(!vp, Ref<Image>(), "Viewport Texture must be set to use it.");
	return RS::get_singleton()->texture_2d_get(vp->texture_rid);
}
void ViewportTexture::_bind_methods() {
	ClassDB::bind_method(D_METHOD("set_viewport_path_in_scene", "path"), &ViewportTexture::set_viewport_path_in_scene);
	ClassDB::bind_method(D_METHOD("get_viewport_path_in_scene"), &ViewportTexture::get_viewport_path_in_scene);
	ADD_PROPERTY(PropertyInfo(Variant::NODE_PATH, "viewport_path", PROPERTY_HINT_NODE_PATH_VALID_TYPES, "SubViewport", PROPERTY_USAGE_DEFAULT | PROPERTY_USAGE_NODE_PATH_FROM_SCENE_ROOT), "set_viewport_path_in_scene", "get_viewport_path_in_scene");
}
ViewportTexture::ViewportTexture() {
	set_local_to_scene(true);
}
ViewportTexture::~ViewportTexture() {
	if (vp) {
		vp->viewport_textures.erase(this);
	}
	ERR_FAIL_NULL(RenderingServer::get_singleton());
	if (proxy_ph.is_valid()) {
		RS::get_singleton()->free(proxy_ph);
	}
	if (proxy.is_valid()) {
		RS::get_singleton()->free(proxy);
	}
}
void Viewport::_sub_window_update_order() {