### 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 (Engine::get_singleton()->is_editor_hint()) {
		set_process_internal(false);
		set_physics_process_internal(false);
	} else if (process_callback == CAMERA2D_PROCESS_IDLE) {
		set_process_internal(true);
		set_physics_process_internal(false);
	} else {
		set_process_internal(false);
		set_physics_process_internal(true);
	}
}
void Camera2D::set_zoom(const Vector2 &p_zoom) {
	
	ERR_FAIL_COND_MSG(Math::is_zero_approx(p_zoom.x) || Math::is_zero_approx(p_zoom.y), "Zoom level must be different from 0 (can be negative).");
	zoom = p_zoom;
	zoom_scale = Vector2(1, 1) / zoom;
	Point2 old_smoothed_camera_pos = smoothed_camera_pos;
	_update_scroll();
	smoothed_camera_pos = old_smoothed_camera_pos;
};
Vector2 Camera2D::get_zoom() const {
	return zoom;
};
Transform2D Camera2D::get_camera_transform() {