$ git clone -n https://src.fedoraproject.org/rpms/libpng.git /var/lib/mock/f40-build-2242145-53669/root/chroot_tmpdir/scmroot/libpng
Cloning into '/var/lib/mock/f40-build-2242145-53669/root/chroot_tmpdir/scmroot/libpng'...
$ git fetch origin 7fb15c2e899d0cfd6de5564e7853f19cc8a15e78:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/libpng
 * [new ref]         7fb15c2e899d0cfd6de5564e7853f19cc8a15e78 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 7fb15c2 Update to libpng 1.6.40