$ git clone -n https://src.fedoraproject.org/rpms/rubygem-imagesize.git /var/lib/mock/f45-build-35029-693/root/chroot_tmpdir/scmroot/rubygem-imagesize
Cloning into '/var/lib/mock/f45-build-35029-693/root/chroot_tmpdir/scmroot/rubygem-imagesize'...
$ git fetch origin 0263fb2a7265c37b5128075bf9a5ebd2053fdc9a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-imagesize
 * [new ref]         0263fb2a7265c37b5128075bf9a5ebd2053fdc9a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 0263fb2 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild