docstr: 把 self.model 的模型参数值同步到 self.target_model
          
code: def sync_target(self):
      """把 self.model 的模型参数值同步到 self.target_model"""
      self.model.sync_weights_to(self.target_model)
  
file_path: PARL/examples/tutorials/parl2_dygraph/lesson3/dqn/algorithm.py
imports: import copy
  import parl
  import paddle
label_desc: Use image node_id 4 for calling the DQN obj's underlying member method code with example usage: obj.sync_target() without return types