* ci: every system on x64 and arm64, on the newest runner images
The desktop app is packaged, and the known-answer workloads checked, on
Ubuntu 26.04, Windows 2025 and Windows 11, and macOS 26, each on x64 and
on arm64. Jobs name their image rather than -latest, download-artifact
moves to v8, and Dependabot keeps actions, Go modules and the desktop's
packages current.
* fix: verify unpacked packages on arm64
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Co-authored-by: excho0 <realexcho@gmail.com>