fix(vuepress): set NODE_ENV before loading bundler in bin shorthands - #1723

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