website/shared/releases: Add missing version macro for FreeBSD 14.2

The website currently fails to render the macro and presents a confusing
"FreeBSD {rel142-current}-STABLE" and incorrect links.

PR: 282652
Reported by: Graham Perrin <grahamperrin@gmail.com>
Reviewed by: cperciva, jrm
Differential Revision: https://reviews.freebsd.org/D47499