chore: update GitHub Actions for Node 24

[marandaneto]

💡 Motivation and Context

Update the remaining release and CI workflow actions that still resolve to Node 20 and add an .nvmrc for local Node 24 parity.

💚 How did you test it?

• Parsed .github/workflows/ci.yml and .github/workflows/release.yml with Ruby YAML.load_file
• Ran git diff --check

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file
• Added the release label to the PR

[github-actions]

posthog-elixir Compliance Report

Date: 2026-04-16 15:58:10 UTC
Duration: 193ms

⚠️ Some Tests Failed

0/1 tests passed, 1 failed

---

Feature_Flags Tests

⚠️ 0/1 tests passed, 1 failed

View Details

Test	Status	Duration
Request Payload.Request With Person Properties Device Id	❌	6ms

Failures

request_payload.request_with_person_properties_device_id

404, message='Not Found', url='http://sdk-adapter:8080/get_feature_flag'