Add sync_session_class to the stubs (#167)

This is for after sqlalchemy/sqlalchemy#6689 is closed

Author: CaselIT

sqlalchemy-stubs/ext/asyncio/session.pyi

@@ -183,12 +183,14 @@ class AsyncSession(
     dispatch: Any = ...
     binds: Any = ...
     sync_session: Session = ...
+    sync_session_class: Type[Session] = ...
     def __init__(
         self,
         bind: Optional[Union[AsyncConnection, AsyncEngine]] = ...,
         binds: Optional[
             Mapping[object, Union[AsyncConnection, AsyncEngine]]
         ] = ...,
+        sync_session_class: Type[Session] = ...,
         **kw: Any,
     ) -> None: ...
     async def run_sync(