fix: resolve mypy narrowing error and pass invocation_id in web server

Signed-off-by: Akshat Kumar <akshat230405@gmail.com>

Author: Akshat8510

src/google/adk/cli/adk_web_server.py

@@ -1498,6 +1498,7 @@ async def run_agent(req: RunAgentRequest) -> list[Event]:
               session_id=req.session_id,
               new_message=req.new_message,
               state_delta=req.state_delta,
+              invocation_id=req.invocation_id,
           )
       ) as agen:
         events = [event async for event in agen]

src/google/adk/runners.py

@@ -496,7 +496,7 @@ async def _run_with_trace(
     ) -> AsyncGenerator[Event, None]:
       with tracer.start_as_current_span('invocation'):
         session = await self._get_or_create_session(
-            user_id=cast(str, user_id), session_id=cast(str, session_id)
+            user_id=user_id, session_id=session_id
         )
 
         if not invocation_id and not new_message: