Fix CPU FlashAttention disabled on Linux/aarch64 by detecting L2 cache via cpuinfo - #29621

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: microsoft/onnxruntime-github-actions/setup-build-tools@v0.0.9. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/