ci: use GH_TOKEN for Homebrew release workflows

[kdy1]

Summary

• standardize Homebrew release workflow authentication on secrets.GH_TOKEN
• update the nodeup, derun, and dexdex release workflows to stop referencing HOMEBREW_TAP_GH_TOKEN
• keep the update-homebrew.sh fallback unchanged for backward compatibility

Testing

• rg -n "HOMEBREW_TAP_GH_TOKEN|secrets.GH_TOKEN" .github/workflows scripts/release/update-homebrew.sh
• `ruby -e 'require "yaml"; [".github/workflows/release-nodeup.yml", ".github/workflows/release-derun.yml", ".github/workflows/release-dexdex.yml"].each { |path| YAML.load_file(path); puts "OK #{path}" }'