rules.pl: add Trust+2 check and disallow self-code-review For golang/go#40699. Change-Id: I681f08cb84aa9bf4b227188594ea02c2727b3697 Reviewed-on: https://go-review.googlesource.com/c/All-Projects/+/254799 Reviewed-by: Andrew Bonventre <andybons@google.com>