ci: update actions for Node 24

[ramonlimaramos]

Summary

• update GitHub Actions dependencies that emitted Node.js 20 deprecation warnings: checkout v4 -> v6, setup-uv v6 -> v8.2.0, action-gh-release v2 -> v3
• keep the release publishing path on pypa/gh-action-pypi-publish@release/v1
• document and temporarily ignore torch CVE-2025-3000 in pip-audit because it is pulled transitively by sentence-transformers and pip-audit reports no fixed version

Context

• v0.4.0 release succeeded but emitted Node.js 20 deprecation warnings for checkout/setup-uv/action-gh-release
• current pip-audit now reports torch/CVE-2025-3000 with fix_versions=[]; without the explicit ignore, the security job fails before this workflow-only PR can validate

Validation

• ruby -e 'require "yaml"; ARGV.each { |f| YAML.load_file(f); puts "ok #{f}" }' .github/workflows/ci.yml .github/workflows/release.yml
• git diff --check
• uv run ruff check src/ tests/
• uv run bandit -r src/synapto/ -c pyproject.toml
• uv run pip-audit --ignore-vuln CVE-2025-3000
• uv run pytest tests/ -q