deps: update dependency gcp-releasetool to v1.8.8#1735

gcf-merge-on-green[bot] merged 2 commits into

googleapis:maingoogleapis/google-http-java-client:mainfrom

renovate-bot:renovate/gcp-releasetool-1.xrenovate-bot/google-http-java-client:renovate/gcp-releasetool-1.xCopy head branch name to clipboard