security/xmlsec1: update to v1.3.9

This unbreaks libxml 2.15, where some pointer types went "const",
and the prior FreeBSD ports version of xmlsec1 wanted to error out
instead of seeing warnings (-Werror) and broke.

ChangeLog: https://www.aleksey.com/xmlsec/news.html
required for:
PR: 291316

(This builds with extant libxml2.14 and 2.15, so let's just commit this.)