$ git clone -n https://src.fedoraproject.org/rpms/R-quantities.git /var/lib/mock/f42-build-side-1-3501321-45974/root/chroot_tmpdir/scmroot/R-quantities
Cloning into '/var/lib/mock/f42-build-side-1-3501321-45974/root/chroot_tmpdir/scmroot/R-quantities'...
$ git fetch origin 3be1f727ef0d0564ad8a8741231aaacf51b160e1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-quantities
 * [new ref]         3be1f727ef0d0564ad8a8741231aaacf51b160e1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 3be1f72 R-maint-sig mass rebuild