Update actions/checkout action to v2

Created by: renovate[bot]

This PR contains the following updates:

Package	Type	Update	New value	References	Sourcegraph
actions/checkout	action	major	v2	source

---

Release Notes

actions/checkout

v2

Compare Source

• Fix default branch resolution for .wiki and when using SSH

---

Configuration

Schedule: "on the 1st through 7th day of the month" in timezone America/Los_Angeles.

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, check this box.

---

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