devel/open62541: Update to 1.3.4 and enable encryption plugins

While we are at it, kill -Werror.
This update fixes the build with LLVM 15.

Changelog: https://github.com/open62541/open62541/releases/tag/v1.3.4

Submitted by: Nico Sonack (maintainer, via email)
Approved by: flo (mentor)
Differential Revision: https://reviews.freebsd.org/D38683