### 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 camera_screen_center;
}
Size2 Camera2D::_get_camera_screen_size() const {
	
	if (Engine::get_singleton()->is_editor_hint() && get_viewport()->get_parent_viewport() == get_tree()->get_root()) {
		return Size2(GLOBAL_GET("display/window/size/viewport_width"), GLOBAL_GET("display/window/size/viewport_height"));
	}
	return get_viewport_rect().size;
}
void Camera2D::set_drag_horizontal_enabled(bool p_enabled) {
	drag_horizontal_enabled = p_enabled;
}
bool Camera2D::is_drag_horizontal_enabled() const {
	return drag_horizontal_enabled;
}
void Camera2D::set_drag_vertical_enabled(bool p_enabled) {
	drag_vertical_enabled = p_enabled;
}
bool Camera2D::is_drag_vertical_enabled() const {
	return drag_vertical_enabled;
}
void Camera2D::set_drag_vertical_offset(real_t p_offset) {
	drag_vertical_offset = p_offset;
	drag_vertical_offset_changed = true;
	Point2 old_smoothed_camera_pos = smoothed_camera_pos;
	_update_scroll();
	smoothed_camera_pos = old_smoothed_camera_pos;
}
real_t Camera2D::get_drag_vertical_offset() const {