Replace corepack with pnpm/action-setup - #250

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@41ff72655975bd51cab0327fa583b6e92b6d3061. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/