We rely on a Github API `/branches` request to determine the active
release trains. Currently this logic is broken if more than 100
protected branches exist within a repository. This issue surfaced
recently where the `items_per_page` setting was set to `30`, causing
the merge tooling and release tooling to not detect the proper "latest"
release train.
This commit uses Github pagination for retrieving branches to determine
the active release trains, and makes the logic more long-term proof.
PR Close#42666
Paul Gschwendtner