Fix block for with_lock, that doesn't yield the receiver

Thanks to @npezza93 for catching this ^_^U

lib/solid_queue/processes/registrable.rb

@@ -53,7 +53,7 @@ def stop_heartbeat
       end
 
       def heartbeat
-        process.with_lock(&:heartbeat)
+        process.with_lock { process.heartbeat }
       rescue ActiveRecord::RecordNotFound
         self.process = nil
         wake_up