v0.15.4 release checklist

[alerque]

• [x] Shuffle any issues being put off to future milestones
• [x] Close all issues in current milestone (except this one)
• [x] Spring clean
  • [x] Re-fetch tooling
• [x] Configure and build
• [x] Pass all tests
  • [x] Remote CI
  • [x] Local
• [x] Cut release
• [x] Push release commit & tag to master
• [x] Download release artifacts, GPG sign, and upload signatures
• [x] Publish release build to craties.io
• Update website
  • [x] Copy and post manual, update 'latest' symlink and menu links
  • [x] Copy changelog and prefix with a summary as a blog post
  • [x] Tweak summary for gfm and edit into GitHub release notes
• Update downstream distro packages
  • [x] Arch Linux: extra/sile
  • [ ] Homebrew: Formula
  • [ ] NixOS: nixpkgs – pull request – tracker
    • [x] Drop devel flag from any website examples that were using it
  • [ ] Ubuntu: ppa
  • [x] Docker Hub: tags
  • [x] GHCR: versions
  • [ ] openSUSE: pinging @Pi-Cla re specfile – merge request
  • [ ] Fedora: pinging @hegjon re copr
  • [ ] NetBSD: pinging @jsonn re pkgsrc
  • [ ] Void Linux:
  • [ ] OpenBSD:
• Bump downstream projects
  • [ ] FontProof (Docker image base plus CI matrix)
  • [x] CaSILE (check, consider patch release)
• [ ] Eat cake

Previous checklist: #2060 (release) This release