Move private-cluster integration test to 1ES pipeline - #549

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: Azure/setup-kubectl@776406bce94f63e41d621b960d78ee25c8b76ede. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/