$ git clone -n https://src.fedoraproject.org/rpms/rubygem-gtk3.git /var/lib/mock/f40-build-734059-105713/root/chroot_tmpdir/scmroot/rubygem-gtk3
Cloning into '/var/lib/mock/f40-build-734059-105713/root/chroot_tmpdir/scmroot/rubygem-gtk3'...
$ git fetch origin 2e0ee46e770d32d5baf381892f1f9e8e995bc063:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-gtk3
 * [new ref]         2e0ee46e770d32d5baf381892f1f9e8e995bc063 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2e0ee46 4.2.0 entry