[ONNX] Update onnx submodule (#47366)
Summary:
Update onnx submodule to 1.8 release
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47366
Reviewed By: hl475
Differential Revision: D24968733
Pulled By: houseroad
fbshipit-source-id: 2f0a3436ab3c9380ed8ff0887a483743c1209721
