net-mgmt/zabbix4-server: Update to 4.0.29

Changelog: https://www.zabbix.com/rn/rn4.0.29

PR: 253825
Submitted by: pg@pakhom.spb.ru (maintainer)
Reviewed by: osa (mentor)
Approved by: osa (mentor)
MFH: 2021Q1
Differential Revision: https://reviews.freebsd.org/D28976