net-mgmt/prometheus-bird-exporter: Update to 1.4.4

Upstream changelog:
https://github.com/czerwonk/bird_exporter/compare/1.4.3...v1.4.4

Reviewed by: arrowd
Approved by: arrowd (ports)
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D54030