chore(ci): update GitHub Actions to Node.js 24 compatible versions

[davidkonigsberg]

Description

Addresses the Node.js 20 deprecation warnings surfaced in this CI run. GitHub is forcing JavaScript actions onto Node 24 on June 2, 2026, and Node 20 reaches EOL in April 2026 — this PR bumps every action in .github/ that has a Node 24–compatible release available.

Changes Made

Bumped the following actions across .github/workflows/*.yml and .github/actions/cached-seed/action.yaml:

• actions/cache@v4 → @v5
• actions/checkout@v4 → @v6 (in release-software.yml)
• actions/upload-artifact@v4 → @v6
• actions/download-artifact@v4 → @v7
• docker/login-action@v3 → @v4
• softprops/action-gh-release@v2 → @v3

Files touched: ci.yml, ci-dynamic-snippets.yml, benchmark-baseline.yml, seed.yml, cli-release.yml, publish-snippets-core.yml, release-software.yml, test-definitions.yml, update-test.yml, cached-seed/action.yaml.

Actions intentionally not bumped

These actions are still in use but have no Node 24 release yet, so their deprecation warnings will persist until upstream ships an update:

• bufbuild/buf-setup-action@v1.50.0 (latest, still node20)
• crs-k/stale-branches@v8.2.2 (latest, still node20)

tj-actions/changed-files@v47 is already on Node 24 (migrated in v47.0.0), so no change needed there.

Review checklist

• Major version bumps — upload-artifact v4→v6, download-artifact v4→v7, cache v4→v5, checkout v4→v6, docker/login-action v3→v4, softprops/action-gh-release v2→v3 are all major bumps. Confirm no breaking input/output changes affect our usage. Notably, upload-artifact v5+ produces immutable artifacts; matched with download-artifact@v7 they should interop correctly.
• Self-hosted runner — update-test.yml uses runs-on: Test. Node 24 requires Actions Runner ≥ 2.327.1 — confirm the self-hosted runner is updated (GitHub-hosted runners are fine).
• Tested via CI only (YAML-only change).

Link to Devin session: https://app.devin.ai/sessions/b24269a1f97f43f9ae84b9029af20dd9
Requested by: @davidkonigsberg

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