Eagerly close subscribed connection

Fix: #1259

Otherwise we need to wait for GC to close it.

lib/redis.rb

@@ -175,6 +175,7 @@ def _subscription(method, timeout, channels, block)
           @subscription_client.send(method, *channels, &block)
         end
       ensure
+        @subscription_client&.close
         @subscription_client = nil
       end
     else