$ git clone -n https://src.fedoraproject.org/rpms/rubygem-railties.git /var/lib/mock/f39-build-1821314-41841/root/chroot_tmpdir/scmroot/rubygem-railties
Cloning into '/var/lib/mock/f39-build-1821314-41841/root/chroot_tmpdir/scmroot/rubygem-railties'...
$ git fetch origin f81fd59f8c25811e5d46bb2d0697db2d96ebaaf8:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-railties
 * [new ref]         f81fd59f8c25811e5d46bb2d0697db2d96ebaaf8 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f81fd59 Enable tests