fix: stabilize release build workflow

[cxymds]

Summary

• switch RustFS binary downloads to upstream GitHub release assets
• align release/tag handling and GitHub Release upload logic
• update Intel macOS runner label and fix downloaded asset filename handling

Validation

• ruby -e 'require "yaml"; YAML.load_file(".github/workflows/build.yml"); YAML.load_file(".github/workflows/upstream-sync.yml"); puts "yaml ok"'
• gh api 'repos/rustfs/rustfs/releases/tags/1.0.0-beta.7' --jq '.assets[].name' | rg 'rustfs-(macos-aarch64|macos-x86_64|windows-x86_64)-latest\.zip'
• git diff --check
• Triggered GitHub Actions run on branch: 27008211385 (confirmed TLS issue resolved and followed up with asset filename fix)