Reformat Markdown code blocks (#12795)

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: UltralyticsAssistant <web@ultralytics.com>

docs/en/modes/export.md

@@ -56,11 +56,11 @@ Export a YOLOv8n model to a different format like ONNX or TensorRT. See Argument
         from ultralytics import YOLO
 
         # Load a model
-        model = YOLO('yolov8n.pt')  # load an official model
-        model = YOLO('path/to/best.pt')  # load a custom trained model
+        model = YOLO("yolov8n.pt")  # load an official model
+        model = YOLO("path/to/best.pt")  # load a custom trained model
 
         # Export the model
-        model.export(format='onnx')
+        model.export(format="onnx")
         ```
 
     === "CLI"