$ git clone -n https://src.fedoraproject.org/rpms/R-V8.git /var/lib/mock/f38-build-side-42-init-devel-1000078-29272/root/chroot_tmpdir/scmroot/R-V8
Cloning into '/var/lib/mock/f38-build-side-42-init-devel-1000078-29272/root/chroot_tmpdir/scmroot/R-V8'...
$ git fetch origin f5543910b2e23de36a9ca8ae2ca04d3a2c143432:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-V8
 * [new ref]         f5543910b2e23de36a9ca8ae2ca04d3a2c143432 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at f554391 Update to latest version (#2185377)