[HOTFIX] Fix the bug in zhipu api with streaming text (#461)

src/agentscope/models/response.py

@@ -53,7 +53,7 @@ def text(self) -> str:
  if self._text is None:
  if self.stream is not None:
  for _, chunk in self.stream:
- self._text += chunk
+ self._text = chunk
  return self._text
 
  @text.setter