po.t: fix expected results

As index.{es,fr} don't exist, po::refreshpofiles copies them from the basewiki
underlay before running msgmerge. msgmerge marks as obsolete the translation
strings that came from the basewiki po files, but the link plugin
does not make the difference between obsolete and up-to-date links.

$links{'index.fr'} and $links{'index.es'} are therefore expected to contain
SandBox and ikiwiki.