Cleanup the accept HTTP header as GitHub no longer versions this

[nunoplopes]

See this: https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api?apiVersion=2022-11-28#media-types

GitHub not longer versions the accept header. It uses this instead: https://docs.github.com/en/rest/about-the-rest-api/api-versions?apiVersion=2022-11-28 But since GitHub is only exposing a single API right now, there's no need for versioning. Plus, all the exported functions are available and are not in preview anymore.