collab: Upsert users by `github_user_id` instead of `github_login` (#16706)
Marshall Bowers
created
This PR makes it so users are upserted by their `github_user_id` instead
of by their `github_login`.
The `github_user_id` is a stable identifier that does not change, while
the `github_login` can change.
In practice we were already using
`get_or_create_user_by_github_account`, which already checks for an
existing user with a `github_user_id` first, so this change doesn't
result in a change in behavior.
This change is primarily for correctness in the event that `create_user`
is called directly, as we want to be upserting by the stable identifier.
Release Notes:
- N/A