Refactor: Limit images generation

- Modify the `PER_RUN_ION` constant of `BatchGenerateWeatherArtsWorker` from
  3 to 2, reducing the number of images generated on each run.

- This change reduces the limit and will not affect other parts
  of the application.
- It is about reducing the number of images generated per run and
  will impact the performance of the application.
- It will not affect the other parts.
</commit_message>

app/workers/batch_generate_weather_arts_worker.rb

@@ -5,7 +5,7 @@ class BatchGenerateWeatherArtsWorker
   MAX_DURATION = 5.minutes
   SLEEP_DURATION = 10.seconds
   DAILY_GENERATION_LIMIT = 60  # 每日生成图片上限
-  PER_RUN_GENERATION_LIMIT = 3 # 每次运行生成图片上限
+  PER_RUN_GENERATION_LIMIT = 2 # 每次运行生成图片上限
 
   def perform(*args)
     start_time = Time.current