$ git clone -n https://src.fedoraproject.org/rpms/rubygem-rack.git /var/lib/mock/f45-build-35261-694/root/chroot_tmpdir/scmroot/rubygem-rack
Cloning into '/var/lib/mock/f45-build-35261-694/root/chroot_tmpdir/scmroot/rubygem-rack'...
$ git fetch origin 4a4be39dfc2832c76b864a79b8914510fee4086a:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/rubygem-rack
 * [new ref]         4a4be39dfc2832c76b864a79b8914510fee4086a -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 4a4be39 Rebuilt for https://fedoraproject.org/wiki/Fedora_45_Mass_Rebuild