$ git clone -n https://src.fedoraproject.org/rpms/R-knitr.git /var/lib/mock/f40-build-2232526-53336/root/chroot_tmpdir/scmroot/R-knitr
Cloning into '/var/lib/mock/f40-build-2232526-53336/root/chroot_tmpdir/scmroot/R-knitr'...
$ git fetch origin b5a802599fd3d77953e6379bca70914643d1bf7a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-knitr
 * [new ref]         b5a802599fd3d77953e6379bca70914643d1bf7a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at b5a8025 1.45