Fix exit code for pytest in case of no matched files #32892
Description
As reported in #31103 comment:44, sage -t xyz fails with exit code 5 if xyz matches no pytest tests. This is fixed.
Component: build
Author: Tobias Diez
Branch/Commit: 89b8754
Reviewer: Julian Rüth
Issue created by migration from https://trac.sagemath.org/ticket/32892