Improve CLA PR Workflow

This is just an advice/suggestion to the maintainers of CPython: we could introduce two labels, CLA signed and CLA not signed, and let the current CLA bot add/remove them based on the status it already checks. The bot already comments on a PR when the CLA is not signed, but this status isn’t visible from the PR list. A reviewer may open a PR, start looking into the issue and changes, and only then notice that the CLA is still pending. Having a label for this would make the status visible upfron...