Ensure %_sourcedir and %_builddir are absolute paths,
as %mkbuilddir will change directories and relative paths will no longer be the same.
Explicitly disable debuginfo packages,
as the test does not work with them
yet they were only implicitly disabled by not using %setup
(which no longer works that way in RPM 4.20+).
Co-authored-by: Michal Domonkos <mdomonko@redhat.com>