$ git clone -n https://src.fedoraproject.org/rpms/ffmpeg.git /var/lib/mock/f41-build-side-1-2811333-32929/root/chroot_tmpdir/scmroot/ffmpeg
Cloning into '/var/lib/mock/f41-build-side-1-2811333-32929/root/chroot_tmpdir/scmroot/ffmpeg'...
$ git fetch origin d4e890a117263d9d6837e22f3da77d1815c837d0:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/ffmpeg
 * [new ref]         d4e890a117263d9d6837e22f3da77d1815c837d0 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at d4e890a Restore bootstrap bcond