chore: Update outdated GitHub Actions versions

[pgoslatara]

This PR updates outdated GitHub Action versions.

• Updated actions/setup-node from v4 to v6 in .github/workflows/release.yml
• Updated actions/checkout from v4 to v6 in .github/workflows/release.yml
• Updated actions/upload-artifact from v4 to v6 in .github/workflows/release.yml
• Updated actions/checkout from v4 to v6 in .github/workflows/changelog.yml
• Updated actions/setup-node from v4 to v6 in .github/workflows/changelog.yml
• Updated actions/setup-node from v3 to v6 in .github/workflows/_test.yml
• Updated actions/checkout from v3 to v6 in .github/workflows/_test.yml

[0xLeif]

Review (via AI-assisted code review): APPROVE

Verified the version bumps in .github/workflows/_test.yml, changelog.yml, and release.yml:

• actions/checkout@v6, actions/setup-node@v6, and actions/upload-artifact@v6 all exist (the v6 major line, running on the Node 24 runtime). setup-node@v6 remains compatible with node-version: 20 as used here.
• Changes are pure uses: version bumps — no YAML structural changes; with: blocks and job syntax are intact.
• PR is based on the current main base SHA, so no staleness concerns.

(Note: submitted as a comment because formal PR review submission is blocked by the org's OAuth App access restrictions.)