Handle Expired Artifacts

[lilly-nathanamorin]

Github Actions build artifacts expire after 90 days:
https://docs.github.com/en/free-pro-team@latest/actions/guides/storing-workflow-data-as-artifacts#:~:text=By%20default%2C%20GitHub%20stores%20build,retention%20period%20can%20be%20customized.

Post to PR should handle that case using the expired return param & notify the user in the PR message that the artifact has expired: https://developer.github.com/v3/actions/artifacts/#list-workflow-run-artifacts