$ git clone -n https://src.fedoraproject.org/rpms/R-prettyunits.git /var/lib/mock/f42-build-side-1-3501318-45974/root/chroot_tmpdir/scmroot/R-prettyunits
Cloning into '/var/lib/mock/f42-build-side-1-3501318-45974/root/chroot_tmpdir/scmroot/R-prettyunits'...
$ git fetch origin ad22cb97472786967adb33a67960d02125ae27ef:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-prettyunits
 * [new ref]         ad22cb97472786967adb33a67960d02125ae27ef -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ad22cb9 R-maint-sig mass rebuild