meta: ensure alphas can be installed by newest nvm - #9316

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda, step-security/harden-runner@f4a75cfd619ee5ce8d5b864b0d183aff3c69b55a. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/