Add allow_forking & allow_update_branch in Repository model

[ledoyen]

It's well hidden in the response schema but it's here :)
https://docs.github.com/en/rest/repos/repos?apiVersion=2022-11-28#get-a-repository

These setting reflects toggles of the same name in the General settings page.

JSON schema extract:

"allow_update_branch": {
    "type": "boolean",
    "examples": [
        true
    ]
},
"allow_forking": {
    "type": "boolean",
    "examples": [
        true
    ]
},

Also present in paths parent, source and template_repository.

[XAMPPRocky]

Thank you for your PR, and congrats on your first contribution! 🎉