Bring back atlas tests for pull_request_target

[nirinchev]

We've removed the Atlas tests from the code_health_fork workflow - we should bring them back in a safe way (review e.g. https://securitylab.github.com/resources/github-actions-preventing-pwn-requests/ for ideas).

While doing that, we should also add CLA checks for external contributions.

[github-actions]

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