fix(prometheus_exporter sink): allow disabling metric expiration via flush_period_secs=0 - #26041

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions-ecosystem/action-add-labels@18f1af5e3544586314bbe15c0273249c770b2daf. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/