An SSL cert can be purchased for as low as $6 a year; if this is important to you, try buying one of those.
Edit: fortunately it looks like certbot plans to support using the old intermediate https://github.com/certbot/certbot/issues/6971 so this should not prove necessary.
Edit: fortunately it looks like certbot plans to support using the old intermediate https://github.com/certbot/certbot/issues/6971 so this should not prove necessary.