Don't mix declarative and scripted pipeline
    
    Agent can't be used in scripted pipeline, which is used by pagure project. This
    means that the label needs to be defined differently as well.
    
    For more info about scripted and declarative Jenkins pipeline see
    https://www.jenkins.io/doc/book/pipeline/#declarative-versus-scripted-pipeline-syntax
    
    Signed-off-by: Michal Konečný <mkonecny@redhat.com>