use `channel_axis` instead.

[CHenYYff]

Loading model from: /root/miniconda3/lib/python3.8/site-packages/lpips/weights/v0.1/vgg.pth
/root/autodl-tmp/pointnerf/run/../run/evaluate.py:11: FutureWarning: multichannel is a deprecated argument name for structural_similarity. It will be removed in version 1.0. Please use channel_axis instead.
return structural_similarity(gt, img, win_size=win_size, multichannel=multichannel)

[Qiangeng Xu]

hi, maybe it is because people have different version of lpips. To retain the best compatibility, it is better to keep the original usage.