*/*: Bump PORTREVISION for known Qt private API abusers

Qt 6.8.2 edition.

These ports directly use or link to a library that uses the Qt
private API and must be rebuilt with every Qt update.

Qt public API/ABI compatability is excellent, so most consumers don't
need to necessarily be rebuilt between patch or even minor releases, but
using the private API is highly discouraged since this is unstable even
between patch releases and is really only meant for internal use.

Adding devel/libqt6xdg and its consumers to the list this time around
based on [1].

PR: 283950 [1]