$ git clone -n https://src.fedoraproject.org/rpms/R-lmtest.git /var/lib/mock/f42-build-side-1-3500328-45970/root/chroot_tmpdir/scmroot/R-lmtest
Cloning into '/var/lib/mock/f42-build-side-1-3500328-45970/root/chroot_tmpdir/scmroot/R-lmtest'...
$ git fetch origin c21aa2fed90010c2a284fc20db95953ad1a7e912:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-lmtest
 * [new ref]         c21aa2fed90010c2a284fc20db95953ad1a7e912 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at c21aa2f R-maint-sig mass rebuild