### 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)
ERR_FAIL_INDEX((int)p_side, 4);
	limit[p_side] = p_limit;
	Point2 old_smoothed_camera_pos = smoothed_camera_pos;
	_update_scroll();
	smoothed_camera_pos = old_smoothed_camera_pos;
}
int Camera2D::get_limit(Side p_side) const {
	ERR_FAIL_INDEX_V((int)p_side, 4, 0);
	return limit[p_side];
}
void Camera2D::set_limit_smoothing_enabled(bool enable) {
	limit_smoothing_enabled = enable;
	_update_scroll();
}
bool Camera2D::is_limit_smoothing_enabled() const {
	return limit_smoothing_enabled;
}
void Camera2D::set_drag_margin(Side p_side, real_t p_drag_margin) {
	ERR_FAIL_INDEX((int)p_side, 4);
	drag_margin[p_side] = p_drag_margin;
	queue_redraw();
}
real_t Camera2D::get_drag_margin(Side p_side) const {
	ERR_FAIL_INDEX_V((int)p_side, 4, 0);
	return drag_margin[p_side];
}
Vector2 Camera2D::get_camera_position() const {