According to the GitHub v3 API reference, generate_release_notes is not a recognised body parameter of the endpoint to update a release. In this library, the value of
RepositoryRelease.GenerateReleaseNotes is passed to the PATCH request to the GitHub API regardless, where it will have no effect.

From what I can tell, RepositoryRelease.GenerateReleaseNotes will only have an effect when calling RepositoriesService.CreateRelease, whereas the comments imply that it has an effect everywhere.

I recognise this field can't have an effect until there is a change in the GitHub API; I think what I would prefer in the meantime would be an update to the code/documentation in this library to make it clear that RepositoriesService.UpdateRelease will not cause release note generation, as this was rather confusing to me when trying to consume this function in a downstream library.