fix(cli): ensure an empty event loop counts as an error

[merceyz]

What's the problem this PR addresses?

If the event loop unexpectedly becomes empty yarn will terminate with exit code 0 even though the command didn't complete successfully.

Ref nodejs/node#53902

Ref #6398 where that happens and the install is incomplete when yarn terminates with exit code 0. It's caught in the following yarn build step which can't find the install state.

How did you fix it?

Set process.exitCode to an error code before executing the CLI so an unexpected empty event loop counts as an error.

Checklist

• I have read the Contributing Guide.
• I have set the packages that need to be released for my changes to be effective.
• I will check that all automated PR checks pass before the PR gets reviewed.