ci: only lint commit messages on PRs (#35035)

As all commit messages are linted during the PR process, we
do not need to relint these previous commit messages on upstream
branches.

PR Close #35035

tools/gulp-tasks/validate-commit-message.js

@@ -10,6 +10,14 @@
 // tslint:disable:no-console
 module.exports = (gulp) => () => {
   try {
+    if (process.env['CIRCLECI'] === 'true' && !process.env['CIRCLE_PR_NUMBER']) {
+      console.info(
+        `Since commit messages are validated as part of the PR review process,\n` +
+        `we do not need to commit messages on CI runs on upstream branches.\n\n` +
+        `Skipping validate-commit-message check`
+        )
+      process.exit();
+    }
     const validateCommitMessage = require('../validate-commit-message');
     const shelljs = require('shelljs');