[ONNX] Wrap 'If' if it has multiple outputs

[karljang]

Without this wrapper, an assertion in from_onnx() will fail with the
error message showing "Number of output mismatch"

The assertion check is here: https://github.com/apache/tvm/blob/main/python/tvm/relay/frontend/onnx.py#L3597

[jwfromm]

Thanks for this fix, it makes sense to me. Can you add a test case that triggers the previous error to tests/python/frontend/onnx/test_forward.py? Take a look at the current test for If and see if you can modify it to optionally have multiple outputs.

[karljang]

@jwfromm
Thanks for the link!
I just modified the current test case to cover multiple output cases~

[jwfromm]

LGTM, thanks for adding these tests. I think you just need to fix some formatting to pass CI's sanity check. You can do that by running make format or black whatever.py.

[karljang]

@jwfromm
Fixed the formatting issues, thank you for your review and tips~

[jwfromm]

@karljang This is now merged. Thanks for taking the initiative to make this fix and congrats on your first commit!

[karljang]

@jwfromm
Thank you! It was a pleasant, first commit for me, thanks to your help.