mt7612u: drain EP 4 when an MCU reply is late, so RXDCOC cannot stall bring-up - #510

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/