chore(build): GitHub Actions checkout@v2

[sullis]

see: https://github.com/actions/checkout/blob/master/README.md

[spinnakerbot]

The following commits need their title changed:

• 1ef3190: GitHub Actions checkout@v2

Please format your commit title into the form:

<type>(<scope>): <subject>, e.g. fix(kubernetes): address NPE in status check

This allows us to easily generate changelogs & determine semantic version numbers when cutting releases. You can read more about commit conventions here.