[releng] Switch to Sirius Web 2026.7.3 - #2461

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02, cypress-io/github-action@6c143abc292aa835d827652c2ea025d098311070. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/