branch discovery without remotes

[mrjf]

github/gh-aw#24345 (comment)

This branch discovery relies on git branch -r --list origin/autoloop/, but the workflow does not fetch remote heads beyond the default checkout. With the default actions/checkout fetch depth, those remote-tracking refs typically aren’t present, so this will often report no branches. Fetch autoloop/ refs explicitly before listing, or use git ls-remote --heads to discover branches without relying on pre-fetched refs.