The documentation for required_workflows endpoints has disappeared from the docs site (formerly seen at https://docs.github.com/en/rest/actions/required-workflows). I found a note on https://docs.github.com/en/actions/using-workflows/required-workflows that says:

Note: Required workflows for GitHub Actions are in private beta and are not available for new signups. On October 18th, 2023, you will no longer be able to access required workflows for GitHub Actions and must use repository rulesets instead. You can read more about this change on the GitHub blog. For more information about repository rulesets, see "About rulesets."

Not sure how go-github should reflect that. Those endpoints never shipped on ghes, so there isn't a need to maintain them for compatibility there. Maybe remove the endpoints from go-github some time after October 18.