Bump django from 5.1.5 to 5.2.16 in /sample-apps/django-postgres-gunicorn - #691

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/setup-python@v5, AikidoSec/firewall-tester-action@v1.0.15. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/