Used Optional[] as type hint for Python 3.9 compatibility

Author: tieneupin

src/murfey/server/demo_api.py

@@ -142,7 +142,7 @@ def machine_info() -> Optional[MachineConfig]:
 
 @lru_cache(maxsize=5)
 @router.get("/instruments/{instrument_name}/machine")
-def machine_info_by_name(instrument_name: str) -> MachineConfig | None:
+def machine_info_by_name(instrument_name: str) -> Optional[MachineConfig]:
     if settings.murfey_machine_configuration:
         return from_file(Path(settings.murfey_machine_configuration), instrument_name)[
             instrument_name