chore: update generator version to newest release v4.12.0#2142

gcf-owl-bot[bot] wants to merge 10 commits into

mastergoogleapis/synthtool:masterfrom

owl-bot-copy-tests-fixtures-nodejs_mono_repo_with_staging-packages-dlpgoogleapis/synthtool:owl-bot-copy-tests-fixtures-nodejs_mono_repo_with_staging-packages-dlpCopy head branch name to clipboard