$ git clone -n https://src.fedoraproject.org/rpms/R-biglm.git /var/lib/mock/f38-build-725375-99605/root/chroot_tmpdir/scmroot/R-biglm
Cloning into '/var/lib/mock/f38-build-725375-99605/root/chroot_tmpdir/scmroot/R-biglm'...
$ git fetch origin f349116ea815d623e19b2be7b69f4d4f557078d1:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-biglm
 * [new ref]         f349116ea815d623e19b2be7b69f4d4f557078d1 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f349116 Fix BuildRequires