build: configure release builds using multi-scm (#1347)

Source-Link: https://github.com/googleapis/synthtool/commit/8200f932b0f019bb4679adab68776a7ac8c3cc45
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:22e41dd7cd82683fa338b647abcc3a29ddb1b17e800b089adc0bec0a3175312c

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>