Update GitHub Actions to support Node.js 24

[LeeCampbell]

Summary

The CI build produces a deprecation warning: the workflow uses actions/checkout@v4, actions/setup-dotnet@v4, and actions/upload-artifact@v4, all of which run on Node.js 20.

Timeline

• 2 June 2026 — GitHub will force actions to run on Node.js 24 by default.
• 16 September 2026 — Node.js 20 will be removed from runners entirely.

Action required

Update the workflow file(s) to use action versions that support Node.js 24, once available (likely @v5 releases).

Reference

• GitHub changelog: Deprecation of Node.js 20 on GitHub Actions runners
• Observed in PR chore(#161): Drop netstandard2.0 target, support net8.0+ only #164 build annotations