Update actions/checkout action to v2

[renovate[bot]]

This PR contains the following updates:

Package	Update	Change
actions/checkout	major	v1 -> v2

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Release Notes

actions/checkout

### [`v2`](https://togithub.com/actions/checkout/blob/master/CHANGELOG.md#v231) [Compare Source](https://togithub.com/actions/checkout/compare/v1...v2) - [Fix default branch resolution for .wiki and when using SSH](https://togithub.com/actions/checkout/pull/284)

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