[ONNX] Fix `argmin` and `argmax` test cases (#79503)
Part of #79263
The `keepdim` argument is theoretically ignored when `dim` is not specified (See [docs](https://pytorch.org/docs/stable/generated/torch.argmin.html)).
Unfortunately the PyTorch implementation seems to still take it into account, resulting in a non-fully-reduced tensor, which is an undefined behavior. Thus, I add `dim` argument to the tests to make the outputs between PyTorch and ONNX runtime consistent.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79503
Approved by: https://github.com/justinchuby, https://github.com/AllenTiTaiWang, https://github.com/BowenBao
