Publishing the site force-pushes an orphan `pages` branch. Two runs racing can
therefore land out of order and leave `pages` holding the older build, with both
runs green and nothing to indicate the site went backwards.
A `pages-deploy` concurrency group with cancel-in-progress makes a newer push
cancel an older in-flight build rather than queue behind it, so the last push to
land is the one that ends up published.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
