$ git clone -n https://src.fedoraproject.org/rpms/R-rjson.git /var/lib/mock/f45-build-6362-348/root/chroot_tmpdir/scmroot/R-rjson
Cloning into '/var/lib/mock/f45-build-6362-348/root/chroot_tmpdir/scmroot/R-rjson'...
$ git fetch origin 0b2218b9cc443b725449a53241aab91de7d80064:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-rjson
 * [new ref]         0b2218b9cc443b725449a53241aab91de7d80064 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0b2218b Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild