Commit class does not expose the branches-where-head endpoint #1145

It is sometimes required to identify any branches of which a given commit ID is a member of.

GitHub API provides such a method as documented here: https://docs.github.com/en/rest/commits/commits?apiVersion=2022-11-28#list-branches-for-head-commit

Propose adding a new member function branchesWhereHead() to the Commit object to expose this