$ git clone -n https://src.fedoraproject.org/rpms/rubygem-railties.git /var/lib/mock/f42-build-3346801-45002/root/chroot_tmpdir/scmroot/rubygem-railties
Cloning into '/var/lib/mock/f42-build-3346801-45002/root/chroot_tmpdir/scmroot/rubygem-railties'...
$ git fetch origin 0ca1a70d5d6851607df0e2b21793ea9ac1b55ff9:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-railties
 * [new ref]         0ca1a70d5d6851607df0e2b21793ea9ac1b55ff9 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0ca1a70 Unlock Sqlite3 2.x+