chore: add packageManager field for CI

Author: onmax

package.json

@@ -2,6 +2,7 @@
   "name": "astro-single-file",
   "type": "module",
   "version": "1.1.0",
+  "packageManager": "pnpm@10.15.1",
   "description": "Astro integration that allows developers to bundle the CSS and HTML in a single file",
   "author": "maximo <maximo@nimiq.com>",
   "license": "MIT",