util: Fix regex for detecting debuginfo packages
    
    The `re.match` function already anchors the pattern at the start of the
    string, but allows for other characters to continue after match.
    
    This is causing problems with packages like `elfutils-debuginfod-client`
    which are not debuginfo.
    
    Let's be safe and explicitly anchor both start and end.
    
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>