$ git clone -n https://src.fedoraproject.org/rpms/R-png.git /var/lib/mock/f45-build-6304-347/root/chroot_tmpdir/scmroot/R-png
Cloning into '/var/lib/mock/f45-build-6304-347/root/chroot_tmpdir/scmroot/R-png'...
$ git fetch origin 63cbd87c432a0ed46ae939a1e315e50883138045:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-png
 * [new ref]         63cbd87c432a0ed46ae939a1e315e50883138045 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 63cbd87 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild