Add Windows MinGW CI for SFTP/wolfsshd and fix build breaks it found - #1241

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v2, microsoft/setup-msbuild@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/