chore: disable renovate for Node github action YAML configs (#2154)

chore: disable renovate for github action YAML configs

Source-Link: https://github.com/googleapis/synthtool/commit/158d49d854395e4eca4706df556628c418037193
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest@sha256:bdf89cdfb5b791d382184a7a769862b15c38e94e7d82b268c58d40d8952720f2

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