Update session.py

Author: DenisStefanAndrei

src/mcp/shared/session.py

@@ -111,7 +111,7 @@ def __exit__(
             self._entered = False
             if not self._cancel_scope:  # pragma: no cover
                 raise RuntimeError("No active cancel scope")
-            self._cancel_scope.__exit__(exc_type, exc_val, exc_tb)
+            return self._cancel_scope.__exit__(exc_type, exc_val, exc_tb)
 
     async def respond(self, response: SendResultT | ErrorData) -> None:
         """Send a response for this request.