Fixes #36329: Read UI notification cache as JSON

The UI notification data is cached as JSON and when retrieved needs
to also be JSON or else a marshalling error is thrown.

app/services/ui_notifications/cache_handler.rb

@@ -5,20 +5,10 @@ def initialize(user_id = User.current.try(:id))
       @user_id = user_id
     end
 
-    # JSON Payload
     def payload
-      result = cache.read(cache_key)
-      if result
-        logger.debug("Cache Hit: notification, reading cache for #{cache_key}")
-        return result
+      cache.fetch(cache_key, raw: true, expires_in: cache_expiry) do
+        { notifications: notifications }.to_json
       end
-
-      result = { notifications: notifications }.to_json
-
-      logger.debug("Cache Miss: notification, writing cache for #{cache_key}")
-      cache.write(cache_key, result, { raw: true, expires_in: cache_expiry })
-
-      result
     end
 
     def clear