$ git clone -n https://src.fedoraproject.org/rpms/stb.git /var/lib/mock/f42-build-side-1-3499364-45964/root/chroot_tmpdir/scmroot/stb
Cloning into '/var/lib/mock/f42-build-side-1-3499364-45964/root/chroot_tmpdir/scmroot/stb'...
$ git fetch origin 2159015b974a119cacbf86fcfc9b04427afb9389:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/stb
 * [new ref]         2159015b974a119cacbf86fcfc9b04427afb9389 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 2159015 stb_image_resize2 2.13