$ git clone -n https://src.fedoraproject.org/rpms/R-fastmap.git /var/lib/mock/f38-build-724161-99404/root/chroot_tmpdir/scmroot/R-fastmap
Cloning into '/var/lib/mock/f38-build-724161-99404/root/chroot_tmpdir/scmroot/R-fastmap'...
$ git fetch origin e1ce9cfd6ec785d97058a42be3e1a1e4ce5692c2:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-fastmap
 * [new ref]         e1ce9cfd6ec785d97058a42be3e1a1e4ce5692c2 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at e1ce9cf R-maint-sig mass rebuild