fix(sparse-mla-sm120): add topk=256 prefill-dsv4 dispatch (fixes #3828) - #3896

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/labeler@v5. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/