$ git clone -n https://src.fedoraproject.org/rpms/rubygem-eventmachine.git /var/lib/mock/f41-build-775142-13519/root/chroot_tmpdir/scmroot/rubygem-eventmachine
Cloning into '/var/lib/mock/f41-build-775142-13519/root/chroot_tmpdir/scmroot/rubygem-eventmachine'...
$ git fetch origin eab4253ee5e567d01a9f1d25dff24b12dc4a5840:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-eventmachine
 * [new ref]         eab4253ee5e567d01a9f1d25dff24b12dc4a5840 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at eab4253 Eliminate use of obsolete %patchN syntax (#2283636)