$ git clone -n https://src.fedoraproject.org/rpms/R-backports.git /var/lib/mock/f45-build-5975-345/root/chroot_tmpdir/scmroot/R-backports
Cloning into '/var/lib/mock/f45-build-5975-345/root/chroot_tmpdir/scmroot/R-backports'...
$ git fetch origin 320bbe8aee4a51627e9a63d3589f14093e2fac99:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-backports
 * [new ref]         320bbe8aee4a51627e9a63d3589f14093e2fac99 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 320bbe8 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild