dev/core#3662 increase length of import table status message

dev/core#3662 increase length of import table status message

This addresses https://lab.civicrm.org/dev/core/-/issues/3662 but
I think the underlying issue is that it has matched so many contacts, for
some reason, that the list of them is longer than 65,535 characters
so it is addressing a symptom, not the cause. 65,535 characters
feels like it should be long enough but changing to LONGTEXT
for a single field seems harmless so I'm a little on the
fence - but even if it just helps us debug....