$ git clone -n https://src.fedoraproject.org/rpms/beets.git /var/lib/mock/f42-build-60988807-6587310/root/chroot_tmpdir/scmroot/beets
Cloning into '/var/lib/mock/f42-build-60988807-6587310/root/chroot_tmpdir/scmroot/beets'...
$ git fetch origin b2e8e820c260f34bc5b8f6063b5f66ae59af046d:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/beets
 * [new ref]         b2e8e820c260f34bc5b8f6063b5f66ae59af046d -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b2e8e82 rhbz#2283970