Update slack_bolt/context/get_thread_context/get_thread_context.py

Co-authored-by: William Bergamin <wbergamin@salesforce.com>

Author: srtaalej

slack_bolt/context/get_thread_context/get_thread_context.py

@@ -32,7 +32,7 @@ def __call__(self) -> Optional[AssistantThreadContext]:
             return self._thread_context
 
         thread = self.payload.get("assistant_thread")
-        if thread is not None and thread.get("context", {}).get("channel_id") is not None:
+        if isinstance(thread, dict) and thread.get("context", {}).get("channel_id") is not None:
             # assistant_thread_started
             self._thread_context = AssistantThreadContext(thread["context"])
             # for this event, the context will never be changed