Message and comment wording fixes

Peter Eisentraut <peter@eisentraut.org>

Commit: cae90d747969612b6e3778416246840790421527
Author: Peter Eisentraut <peter@eisentraut.org>
Date: 2026-06-25T08:51:22Z
Message and comment wording fixes

Some parts of pg_upgrade referred to "on the old cluster" etc.  Change
that to "in the old cluster", matching existing style.

Files