Enhance error message posted by scm_request_processor
    
    This is enhancement of error message for creating new branch in
    scm_request_processor. This should help analyze the issue that is currently
    happening on https://pagure.io/releng/fedora-scm-requests/issue/50370
    
    Signed-off-by: Michal Konečný <mkonecny@redhat.com>