The script defined a purge_cdn_cache() function but never invoked it,
so every CI run only declared the helper and exited cleanly without
issuing a single curl. The CDN had been relying entirely on the
Cache-Control: no-cache headers R writes onto PACKAGES* objects.
Rewrite to call the purge inline; while here:
- drop `set -x` (leaked the AccessKey header into logs)
- drop the python3 urlencoder; `curl --data-urlencode` does the
same with no Python dep, so the workflow purge step no longer
needs `apk add bash curl` over `curl --data-urlencode`-capable
curl alone
- add `src/contrib/Meta/archive.rds` to the resource list - it
changes during process-updates and was being served stale
