CI: upgrade GitHub Actions to Node.js 24-compatible versions

[sunt05]

Summary

• Upgrade all GitHub Actions to Node.js 24-compatible versions across 13 workflow/action files
• Resolves Node.js 20 deprecation warnings (run 23959741802) before the June 2026 enforcement deadline
• Actions updated: checkout (v6), cache (v5), setup-python (v6), upload-artifact (v7), download-artifact (v8), configure-pages (v6), upload-pages-artifact (v4), deploy-pages (v5)

Test plan

• CI workflows run without Node.js 20 deprecation warnings
• Wheel builds complete on all platforms
• Pages deployment works correctly

🤖 Generated with Claude Code

[github-actions]

CI Build Plan

Changed Files

CI/workflows (3 files)

• .github/actions/build-suews/action.yml
• .github/workflows/build-publish_to_pypi.yml
• .github/workflows/cibuildwheel-debug.yml

Build Configuration

	Configuration
Platforms	Linux x86_64
Python	3.9, 3.14
Test tier	smoke (critical tests only)
QGIS3 UMEP build	Skipped (no ABI changes)
PR status	Ready (standard matrix)

Rationale

• CI/workflow files changed -> validation build
• No compiled extension changes -> QGIS3 UMEP build skipped (nightly provides coverage)

---

_{Updated by CI on each push. See path-filters.yml for category definitions.}

[github-actions]

Preview Deployed

Content	Preview URL
Site	https://suews.io/preview/pr-1280/
Docs	https://suews.io/preview/pr-1280/docs/

Note

This preview is ephemeral. It will be lost when:

• Another PR with site/ or docs/ changes is pushed
• Changes are merged to master
• A manual workflow dispatch runs

To restore, push any commit to this PR.