feat: add c# solution for lc No.3731 - #5338

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