Update src/mcp/server/streamable_http_manager.py

Co-authored-by: Marcelo Trylesinski <marcelotryle@gmail.com>

Author: felixweinberger

src/mcp/server/streamable_http_manager.py

@@ -80,7 +80,7 @@ def __init__(
         if session_idle_timeout is not None and session_idle_timeout <= 0:
             raise ValueError("session_idle_timeout must be a positive number of seconds")
         if stateless and session_idle_timeout is not None:
-            raise ValueError("session_idle_timeout is not supported in stateless mode")
+            raise RuntimeError("session_idle_timeout is not supported in stateless mode")
 
         self.app = app
         self.event_store = event_store