addons-tests.yml now cancels an older run on master, as the other test
workflows do. addons-package.yml puts all master pushes in one group
without cancelling: a running publish finishes, and a newer queued run
replaces an older queued one. Tag, release and PR runs keep separate
groups. Document both in the workflow headers and .agents/ci-caching.md.
Assisted-by: Claude:claude-sonnet-5-5 python3