Update to actions/checkout@v3

[stuartleeks]

Builds are hitting this warning:

[PR comment](https://github.com/devcontainers/ci/actions/runs/3996901503/jobs/6857532053)
Node.js 12 actions are deprecated. Please update the following actions to use Node.js 16: actions/checkout@v2. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/.

We are currently using actions/checkout@v2 and actions/checkout@v3 is updated to use node 16

[stuartleeks]

Closed by #219