devel/libzim: Support ICU 76.1

The added patch is an upstream's candidate to fix the build against ICU
76.1, and will make it in the next release in this or another form.

In the meantime, adopt it in the ports tree as is as it does not disturb
the build against older versions of ICU.

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

PR: 283542
Sponsored by: The FreeBSD Foundation