[Debian-science-sagemath] Sage 9.1 doesn't build as root

[John Scott]

> Did you make sure that there was no old config.status around when you built
> with this change? The new commit is just this and I checked that the root
> check was not run anymore.

I've cloned Git fresh and tried once more in sbuild where it has failed again. 
Do you have different results? I've done
$ git clone --recursive https://salsa.debian.org/science-team/sagemath.git
$ cd sagemath
$ debian/rules debian/control
$ debian/rules ../sagemath_9.1.orig.tar.xz
$ cd ..
$ sbuild ./sagemath

and it nevertheless whines about being built as root.