devel/kiwix-tools: Depend on devel/libkiwix13

This will allow updating devel/libkiwix to 14.0.0 again without breaking
the build of devel/kiwix-tools, whose latest released version at time of
this writing requires libkiwix 13.

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

Reviewed by: jrm
Fixes: dafb538b3fd6 ("devel/libkiwix: Update to 14.0.0")
MFH: 2025Q1
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D48396