Tiny Nerf Colab Evaluation Bug

[johnmaxh]

It looks like when evaluating the loss in the last cell of the colab, the code uses
loss = torch.nn.functional.mse_loss(rgb_predicted, target_img)

But believe this should actually be
loss = torch.nn.functional.mse_loss(rgb_predicted, testimg)

Since we use testpose for rgb_predicted we should compare to testimg not target_img, which is just a random training sample.