`gh pr checks` should return different exit code for PENDING vs FAILED

[darthwalsh]

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.

[samcoe]

@darthwalsh This seems like a reasonable improvement to the pr checks command. I don't think we want to use exit code 2 as we already use that in other commands to indicate the user cancelled the command but we can introduce a new one for this case.

[rajhawaldar]

@samcoe I will take this ahead.

[darthwalsh]

@rajhawaldar thanks for implementing this! Used a new release of gh today and improved my scripts :D