$ git clone -n https://src.fedoraproject.org/rpms/gthumb.git /var/lib/mock/f45-build-13134-446/root/chroot_tmpdir/scmroot/gthumb
Cloning into '/var/lib/mock/f45-build-13134-446/root/chroot_tmpdir/scmroot/gthumb'...
$ git fetch origin eb7f6f7cfffc368b2f0a572fdf26a58d439622e7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gthumb
 * [new ref]         eb7f6f7cfffc368b2f0a572fdf26a58d439622e7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at eb7f6f7 Update to 4.0.rc