Describe the feature or problem you’d like to solve

Now, gh pr checks fails with exit code 1 if any checks have Failed or are Pending:

From a script, I can't easily tell whether the PR checks have failed, or maybe pass later.

Proposed solution

Document exit code 1 returned if any checks have failed. Return exit code 2 if no checks have failed, but some are pending.

Additional context

Related to #6056 but using exit code is much easier for scripts that JSON.