Explicitly add packageManager to package.json to help dependabot

Without it, we get dependabot warnings "Dependabot does not support
your npm version. Because of this, Dependabot cannot update this pull
request."

Author: mickaelistria

org.eclipse.wildwebdeveloper.tests/testProjects/eslint/package.json

@@ -13,5 +13,6 @@
 		"@typescript-eslint/parser": "^7.18.0",
 		"eslint": "^8.57.1",
 		"typescript": "5.7.3"
-	}
+	},
+  "packageManager": "npm@11"
 }