$ git clone -n https://src.fedoraproject.org/rpms/gnujump.git /var/lib/mock/f42-build-3282786-41399/root/chroot_tmpdir/scmroot/gnujump
Cloning into '/var/lib/mock/f42-build-3282786-41399/root/chroot_tmpdir/scmroot/gnujump'...
$ git fetch origin ba8effb3be8db8d4fd007f75bce1cd26d1b014ea:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/gnujump
 * [new ref]         ba8effb3be8db8d4fd007f75bce1cd26d1b014ea -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at ba8effb Fix FTBFS