chore(deps): update dependency @types/sinon to v9 (#391)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [@types/sinon](https://togithub.com/DefinitelyTyped/DefinitelyTyped) | devDependencies | major | [`^7.5.2` -> `^9.0.0`](https://renovatebot.com/diffs/npm/@types%2fsinon/7.5.2/9.0.0) |

---

### Renovate configuration

:date: **Schedule**: "after 9am and before 3pm" (UTC).

:vertical_traffic_light: **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

:recycle: **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

:no_bell: **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#googleapis/nodejs-tasks).

Author: renovate-bot

packages/google-cloud-tasks/package.json

@@ -49,7 +49,7 @@
   "devDependencies": {
     "@types/mocha": "^7.0.0",
     "@types/node": "^12.0.0",
-    "@types/sinon": "^7.5.2",
+    "@types/sinon": "^9.0.0",
     "c8": "^6.0.0",
     "codecov": "^3.0.2",
     "eslint": "^6.0.0",