Trac #34603: Fix singular spkg-configure

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

}}}

URL: https://trac.sagemath.org/34603
Reported by: mkoeppe
Ticket author(s): Dima Pasechnik
Reviewer(s): Matthias Koeppe

build/pkgs/singular/spkg-configure.m4

@@ -7,7 +7,7 @@ SAGE_SPKG_CONFIGURE([singular], [
       dnl Use pkg-config to ensure that Singular is new enough.
       PKG_CHECK_MODULES([SINGULAR], [Singular >= 4.2.1], [
        AC_MSG_CHECKING([that Singular's help is working])
-       AS_IF([test x`printf "system(\"--browser\", \"builtin\"); \n help;" | Singular 2>&1 | grep "error\ occurred"` = x], [
+       AS_IF([test x`printf "system(\"--browser\", \"builtin\"); \n help;" | Singular 2>&1 | grep "error occurred"` = x], [
         AC_MSG_RESULT(yes)
         dnl We have Singular. Now determine the shared library path on
         dnl platforms on which sage.libs.singular needs to reload the library with RTLD_GLOBAL.