fix mypy error

Author: omkar-334

pyproject.toml

@@ -310,6 +310,7 @@ overrides = [
     "rfdetr.training.callbacks.drop_schedule",
     "rfdetr.training.callbacks.ema",
     "rfdetr.cli.train",
+    "rfdetr.cli.export",
     "rfdetr.training.drop_schedule",
     "rfdetr.training.model_ema",
     "rfdetr.training.module_data",