Fix opening and closing Redis connections instead of using a pool (#18171)

* Fix opening and closing Redis connections instead of using a pool

* Fix Redis connections not being returned to the pool in CLI commands

lib/mastodon/rack_middleware.rb

@@ -19,7 +19,7 @@ class Mastodon::RackMiddleware
   end
 
   def clean_up_redis_socket!
-    Thread.current[:redis]&.close
+    RedisConfiguration.pool.checkin if Thread.current[:redis]
     Thread.current[:redis] = nil
   end