net-mgmt/prometheus-bird-exporter: Update to 1.5.0

Release notes:
https://github.com/czerwonk/bird_exporter/releases/tag/v1.4.5
https://github.com/czerwonk/bird_exporter/releases/tag/v1.5.0

Reviewed by: arrowd
Approved by: arrowd (ports)
Differential Revision: https://reviews.freebsd.org/D57127