Check dnf version before skipping base module conflicts
    
    The base module conflict generation was skipped for local builds
    in 6b2e5be93aad because libdnf wasn't ported to libmodulemd yet -
    that was done in libdnf-0.45, so only warn and skip for versions of
    dnf too old to require libdnf-0.45.
    
    (Don't just unconditionally skip check/warning in case someone is
    doing local module builds on RHEL 8.)