Fix singular spkg-configure #34603
Description
Seen on archlinux-latest, https://github.com/FFY00/meson-python/actions/runs/3146686714/jobs/5115498470
Checking whether SageMath should install SPKG singular...
checking whether any of gmp ntl flint readline mpfr cddlib is installed as or will be installed as SPKG... no
checking for Singular... /usr/sbin/Singular
checking for SINGULAR... yes
checking that Singular's help is working... grep: warning: stray \ before white space
./configure: line 43759: test: too many arguments
no
configure: no suitable system package found for SPKG singular
Component: build: configure
Author: Dima Pasechnik
Branch/Commit: 373bd38
Reviewer: Matthias Koeppe
Issue created by migration from https://trac.sagemath.org/ticket/34603