Update actions/checkout action to v3

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#v302) [Compare Source](https://togithub.com/actions/checkout/compare/v2...v3) - [Add input `set-safe-directory`](https://togithub.com/actions/checkout/pull/770)

Configuration

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Insprill / custom-join-messages

Update actions/checkout action to v3 #25

Release Notes

Configuration