WebUI: temporarily pin dependency

The plugin was causing problems in new versions so pin it with an older
version and look into it later.
Upstream issue: JamieMason/eslint-plugin-prefer-arrow-functions#50

PR #22140.

src/webui/www/package.json

@@ -13,7 +13,7 @@
     "@stylistic/eslint-plugin": "*",
     "eslint": "*",
     "eslint-plugin-html": "*",
-    "eslint-plugin-prefer-arrow-functions": "*",
+    "eslint-plugin-prefer-arrow-functions": "3.4.2",
     "eslint-plugin-regexp": "*",
     "html-validate": "*",
     "js-beautify": "*",