devel/libkiwix*: Support ICU 76.1

This change is similar to what was done to devel/libzim.

It allows to build against ICU 76.1, without disturbing the build
against older versions (e.g., 74.2).

This is a maintainer update (olce.freebsd.ports@certner.fr).

PR:             278420
Sponsored by:   The FreeBSD Foundation