chore: release 2.4.0 (#270)

🤖 I have created a release \*beep\* \*boop\*
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## [2.4.0](https://www.github.com/googleapis/nodejs-cloudbuild/compare/v2.3.2...v2.4.0) (2021-08-16)


### Features

* Add ability to configure BuildTriggers to create Builds that require approval before executing and ApproveBuild API to approve or reject pending Builds ([#267](https://www.github.com/googleapis/nodejs-cloudbuild/issues/267)) ([18ec067](https://www.github.com/googleapis/nodejs-cloudbuild/commit/18ec067ac1e112836c5d56747dda89e04f87c481))
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This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please).

cloudbuild/package.json

@@ -15,7 +15,7 @@
     "test": "c8 mocha system-test --timeout=800000"
   },
   "dependencies": {
-    "@google-cloud/cloudbuild": "^2.3.2"
+    "@google-cloud/cloudbuild": "^2.4.0"
   },
   "devDependencies": {
     "c8": "^7.0.0",