Note: I've finally added a paragraph for this case: https://wiki.debian.org/qa.debian.org/FTBFS/nocheck
Sometimes there is a build-dependency rightly marked <!nocheck> which depends transitively on another package which is always required to build (for example, python3-setuptools). In this case the right solution is to add this missing package as an extra build-dependency, without dropping the <!nocheck> from the package rightly having it. This is why you should take the suggestions from the check-nocheck script with a grain of salt. Thanks a lot.
