chore(deps): update dependency @types/mocha to v9 (#561)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [@types/mocha](https://togithub.com/DefinitelyTyped/DefinitelyTyped) | [`^8.0.0` -> `^9.0.0`](https://renovatebot.com/diffs/npm/@types%2fmocha/8.2.3/9.1.1) | [![age](https://badges.renovateapi.com/packages/npm/@types%2fmocha/9.1.1/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/npm/@types%2fmocha/9.1.1/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/npm/@types%2fmocha/9.1.1/compatibility-slim/8.2.3)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/npm/@types%2fmocha/9.1.1/confidence-slim/8.2.3)](https://docs.renovatebot.com/merge-confidence/) |

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packages/google-cloud-iot/package.json

@@ -46,7 +46,7 @@
     "google-gax": "^2.24.1"
   },
   "devDependencies": {
-    "@types/mocha": "^8.0.0",
+    "@types/mocha": "^9.0.0",
     "@types/node": "^16.0.0",
     "@types/sinon": "^10.0.0",
     "c8": "^7.2.1",