Install into /usr/lib rather than /usr/lib64/
In koji-1.22.0-129-g0ef3c751 I've changed the way how
site-packages directory is obtained. What I did not realize back
then is there can be multilib systems which will not search for
packages in /usr/lib64. But 64bit systems do look into /usr/lib.
Therefore, let's pick the location where both systems work.
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1894261
Fixes: #2578
https://pagure.io/koji/issue/2578
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>