Branch Protection w/o required PR review allowed by Github but not API
The Github web GUI allows you to create branch protection rules without requiring pull request reviews - disallowing delete/force push and limiting the entities that can merge changes, but not requiring a PR which in our case happens elsewhere in the pipeline. It does not seem possible to express this to the UpdateBranchProtection() function in go-github - if I leave required_pull_request_reviews null then I get a validation error.
This sounds like a good question to ask GitHub tech support. If the GitHub v3 API can not perform what you want, then this Go client library will certainly not be able to either.
Please contact GitHub tech support with your question and report your findings back here. Thank you.