ci: fix pnpm version mismatch

NOTE: it reads the desired one from package.json

Author: lorenzocorallo

.github/workflows/preview.yml

@@ -43,7 +43,6 @@ jobs:
 
       - uses: pnpm/action-setup@v4
         with:
-          version: 9
           run_install: false
 
       - name: Get pnpm store directory