Adding repo allowupdatebranch

[michal-ciechan]

As per https://docs.github.com/en/rest/repos/repos#update-a-repository, there is the following setting:

allow_update_branch boolean
Either true to always allow a pull request head branch that is behind its base branch to be updated even if it is not required to be up to date before merging, or false otherwise.

Default: false

• Code change
• Locally tested
• Fix existing Unit/Integration Tests
• Add new unit/integration tests

[nickfloyd]

This looks good! Thanks for the changes! ❤️ Given that our serialization and other tests cover this response model, we should be good.