Use pnpm.js to install pnpm

package.json

@@ -11,10 +11,12 @@
     "expand-tilde": "^2.0.2",
     "js-yaml": "^4.0.0",
     "ajv": "^6.12.5",
+    "fs-extra": "^9.1.0",
     "@actions/core": "^1.2.6",
     "@types/expand-tilde": "^2.0.0",
     "@types/node-fetch": "^2.5.8",
     "@types/js-yaml": "^4.0.0",
+    "@types/fs-extra": "^9.0.8",
     "@types/node": "^14.14.35"
   },
   "devDependencies": {