ci: build x86 musl release on hosted Ubuntu

[cbusillo]

Summary

• move the x86_64 musl release build from the passworded self-hosted runner to hosted ubuntu-24.04
• keep the target and artifact name unchanged so release packaging behavior stays the same

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/release.yml"); puts "yaml ok"'\n- git diff --check\n- ./build-fast.sh\n\nRefs Plan Every Code default branch and release identity #87