chore: update workflow actions

[rlippmann]

Summary

• update GitHub Actions used by CI to current non-Node-20-deprecated majors
• keep workflow behavior, matrices, and validation commands unchanged

Why

GitHub Actions was reporting Node.js 20 deprecation warnings during CI runs. This updates the affected actions to newer majors that run on the current GitHub Actions runtime.

Scope checklist

• Diff is minimal and scoped to the requested behavior
• No workflow logic changes
• No matrix changes
• No validation command changes
• No unrelated refactors

Notes

This is a workflow-only maintenance update intended to remove GitHub Actions deprecation warnings.