fix(toolkit-lib): downstream stack selection uses wrong key for nested stacks - #1835

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: cdklabs/pr-triage-manager@main. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/