$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rspec.git /var/lib/mock/f40-build-2639309-66352/root/chroot_tmpdir/scmroot/rubygem-rspec
Cloning into '/var/lib/mock/f40-build-2639309-66352/root/chroot_tmpdir/scmroot/rubygem-rspec'...
$ git fetch origin e9c91c8536f40c80916d11456069fa083aaa34b2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rspec
 * [new ref]         e9c91c8536f40c80916d11456069fa083aaa34b2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e9c91c8 3.13.0