The value was defined 3 years ago, in March 2017 when there were much
    fewer modules in Fedora. Our Koji has capacity to run many more builds.
    Currently we have 158 Koji builders in default channel that are able to
    run RPM builds. Their total capacity is 566. Therefore it should be safe
    to increase MBS NUM_CONCURRENT_BUILDS to at least 100. Especially since
    Koji builds submitted by MBS have lower priority than default for
    non-modular component builds submitted by packagers, so
    packager-submitted builds will tak precedence over builds submitted by
    MBS.
    
    Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>