test-pr: Improve test detection
    
    `git log` tends to short cut filename if the output is not a terminal.
    
    Fixes:
    
        git log --format= --stat HEAD -1 | grep '/' | sed 's#^ \(.*\)/.*#\1#' | sort -u | tr '\n' ' ' | xargs
        .../bz481628-send-msg-to-dbus selinux-policy/bz481628-send-msg-to-dbus