release_notes.py: skip issues labeled github_actions or skip-changelog

Issues with these labels (e.g. Dependabot bumps, automated license updates)
are noise in the changelog. The script now filters them out and logs the
skipped items to stderr so the omission is visible.

Also label automated license-update PRs with skip-changelog in the workflow
so they are excluded automatically in future runs.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>