### 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)
camera_screen_center = screen_rect.get_center();
	Transform2D xform;
	xform.scale_basis(zoom_scale);
	if (!ignore_rotation) {
		xform.set_rotation(camera_angle);
	}
	xform.set_origin(screen_rect.position);
	return (xform).affine_inverse();
}
void Camera2D::_notification(int p_what) {
	switch (p_what) {
		case NOTIFICATION_INTERNAL_PROCESS:
		case NOTIFICATION_INTERNAL_PHYSICS_PROCESS: {
			_update_scroll();
		} break;
		case NOTIFICATION_TRANSFORM_CHANGED: {
			if (!is_processing_internal() && !is_physics_processing_internal()) {
				_update_scroll();
			}
		} break;
		case NOTIFICATION_ENTER_TREE: {
			ERR_FAIL_COND(!is_inside_tree());
			if (custom_viewport && ObjectDB::get_instance(custom_viewport_id)) {
				viewport = custom_viewport;
			} else {
				viewport = get_viewport();
			}
			canvas = get_canvas();
			RID vp = viewport->get_viewport_rid();
			group_name = "__cameras_" + itos(vp.get_id());