Update actions/checkout action to v3

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	major	v2 -> v3

---

Release Notes

actions/checkout

### [`v3`](https://togithub.com/actions/checkout/blob/HEAD/CHANGELOG.md#v310) [Compare Source](https://togithub.com/actions/checkout/compare/v2...v3) - [Use @​actions/core `saveState` and `getState`](https://togithub.com/actions/checkout/pull/939) - [Add `github-server-url` input](https://togithub.com/actions/checkout/pull/922)

---

Configuration

📅 Schedule: Branch creation - "before 3am on Monday" (UTC), Automerge - At any time (no schedule defined).

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

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

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

---

• [ ] If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by Mend Renovate. View repository job log here.