chore(deps): update actions/checkout action to v3 (#767)

[![WhiteSource Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://togithub.com/actions/checkout) | action | major | `v2` -> `v3` |

---

### Release Notes

<details>
<summary>actions/checkout</summary>

### [`v3`](https://togithub.com/actions/checkout/compare/v2...v3)

[Compare Source](https://togithub.com/actions/checkout/compare/v2...v3)

</details>

---

### Configuration

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

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

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

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

---

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

---

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