The self-tests, the build-isolation fixture and the three tracker
workflows pulled archlinux:base-devel from Docker Hub without logging
in. On 2026-10-09 that failed two jobs on one pull request: one with
'toomanyrequests', one with a 504 from Docker Hub's token endpoint.
Arch publishes the same image as ghcr.io/archlinux/archlinux, which
GitHub's runners pull without that limit.