Clarify evaluation of check values reported concurrently from multiple sources

[fjeldstad]

Code of Conduct

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What article on docs.github.com is affected?

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/collaborating-on-repositories-with-code-quality-features/about-status-checks

What part(s) of the article would you like to see updated?

I think there is a need for a new section that explains how multiple sources of values for a given check are evaluated. In particular, it is very important for users to understand that the branch protection feature will not wait for all running workflows to complete execution before setting the outcome of a specific check.

If I would write the section myself, it could be something along these lines:

Evaluation of concurrently reported check values

It is possible for multiple sources to report values for the same check. A common example would be GitHub Actions workflows with a job named corresponding to a required check.
For example, let's say a branch has a required check called test. If there are multiple workflows each with a job named test, they will all eventually contribute to the
final value of the check. If one of them fails, the check will be marked as failed, as you would expect. But the check engine will not wait for all workflows to finish before
evaluating the check value - it will aggregate values as they are reported; a check might be first marked as successful by a quick workflow just to later be changed
to failed by a slower workflow. In other words, there can be a time window when a pull request is able to merge even if it would be prevented from doing so by other pending workflows.
This behavior is especially important to be aware of if using the auto-merge feature as pull requests will be merged as soon as the first successful check value is reported.

Additional information

No response

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[nguyenalex836]

@fjeldstad Thank you for raising this issue! I'll get this triaged for review ✨ Our team will provide feedback regarding the best next steps for this issue - thanks for your patience! 💛

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