Add packageManager field to specify pnpm version for CI

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

package.json

@@ -2,6 +2,7 @@
   "name": "objectql-monorepo",
   "private": true,
   "license": "AGPL-3.0",
+  "packageManager": "pnpm@9.15.4",
   "pnpm": {
     "onlyBuiltDependencies": [
       "@nestjs/core",