Update test-project to yarn 4.9.4 and eexplicitly write packageManager 4.9.4

Author: devcontainers-bot

.yarn/install-state.gz

@@ -8,5 +8,6 @@
     "jsonc": "^2.0.0",
     "mkdirp": "0.5.5",
     "rimraf": "^3.0.2"
-  }
+  },
+  "packageManager": "yarn@4.9.4"
 }

package.json

@@ -1,5 +1,6 @@
 {
   "dependencies": {
     "puppeteer": "^5.5.0"
-  }
+  },
+  "packageManager": "yarn@4.9.4"
 }