### 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 (AudioServer::get_singleton()) {
		AudioServer::get_singleton()->notify_listener_changed();
	}
}
void Viewport::set_as_audio_listener_2d(bool p_enable) {
	if (p_enable == is_audio_listener_2d_enabled) {
		return;
	}
	is_audio_listener_2d_enabled = p_enable;
	_update_audio_listener_2d();
}
bool Viewport::is_audio_listener_2d() const {
	return is_audio_listener_2d_enabled;
}
AudioListener2D *Viewport::get_audio_listener_2d() const {
	return audio_listener_2d;
}
void Viewport::enable_canvas_transform_override(bool p_enable) {
	if (override_canvas_transform == p_enable) {
		return;
	}
	override_canvas_transform = p_enable;
	if (p_enable) {
		RenderingServer::get_singleton()->viewport_set_canvas_transform(viewport, find_world_2d()->get_canvas(), canvas_transform_override);
	} else {
		RenderingServer::get_singleton()->viewport_set_canvas_transform(viewport, find_world_2d()->get_canvas(), canvas_transform);
	}
}
bool Viewport::is_canvas_transform_override_enbled() const {