For example on ubuntu-trusty-maximal (https://github.com/mkoeppe/sage/runs/2135025659),
configure correctly finds system perl_cpan_polymake_prereq
but then tests whether SPKG perl_cpan_polymake_prereq can be installed (it gives an error - by design).

This can be distracting in the GH Action logs.

Depends on #31163

CC: @kliem @jhpalmieri

Component: porting

Issue created by migration from https://trac.sagemath.org/ticket/31522