$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rgen.git /var/lib/mock/f41-build-1093584-19988/root/chroot_tmpdir/scmroot/rubygem-rgen
Cloning into '/var/lib/mock/f41-build-1093584-19988/root/chroot_tmpdir/scmroot/rubygem-rgen'...
$ git fetch origin e4684e31aebc19cc9139d6709c6f46c7f1a3bd15:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rgen
 * [new ref]         e4684e31aebc19cc9139d6709c6f46c7f1a3bd15 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e4684e3 Eliminate use of obsolete %patchN syntax (#2283636)