Feature request: add tree field to Commit

Hi there,

I am currently trying to get the git tree from a specific repository's default branch, but it fails because Commit does not have the `tree` property

The tree property is officially documented, hence it would be great if GitHub.jl could support it 
https://docs.github.com/en/rest/git/commits?apiVersion=2022-11-28#get-a-commit

