$ git clone -n https://src.fedoraproject.org/rpms/R-FMStable.git /var/lib/mock/f45-build-5905-345/root/chroot_tmpdir/scmroot/R-FMStable
Cloning into '/var/lib/mock/f45-build-5905-345/root/chroot_tmpdir/scmroot/R-FMStable'...
$ git fetch origin 5a2a6912c4528d801bf10917e9adb528ade84e1a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-FMStable
 * [new ref]         5a2a6912c4528d801bf10917e9adb528ade84e1a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 5a2a691 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild