use pnpm for prebuild script

Author: mansona

scripts/update-prebuild.mjs

@@ -24,7 +24,7 @@ if (anyChanges.stdout) {
 shell.exec('git clean -xdf');
 
 // this can't use shell.js because we cleared node_modules
-await exec('npm i');
+await exec('pnpm i');
 
 shell.exec('rm -r public/assets/*');
 shell.exec('rm -rf public/v*');