Update onnx>=1.12.0 (#10526)

export.py

@@ -132,7 +132,7 @@ def export_torchscript(model, im, file, optimize, prefix=colorstr('TorchScript:'
 @try_export
 def export_onnx(model, im, file, opset, dynamic, simplify, prefix=colorstr('ONNX:')):
     # YOLOv5 ONNX export
-    check_requirements('onnx')
+    check_requirements('onnx>=1.12.0')
     import onnx
 
     LOGGER.info(f'\n{prefix} starting export with onnx {onnx.__version__}...')