$ git clone -n https://src.fedoraproject.org/rpms/yarnpkg.git /var/lib/mock/f40-build-794282-139514/root/chroot_tmpdir/scmroot/yarnpkg
Cloning into '/var/lib/mock/f40-build-794282-139514/root/chroot_tmpdir/scmroot/yarnpkg'...
$ git fetch origin 6e3f039e6a0c23ce3ebcad526a5306c409bdbfac:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/yarnpkg
 * [new ref]         6e3f039e6a0c23ce3ebcad526a5306c409bdbfac -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 6e3f039 Repackage bundle without bundled binaries, use npm to build