Model in training mode during demo.py

[braydenrudisill]

Model.eval() needs to be added in the demo.py for the model be in evaluation mode. Being stuck in training mode enables this line of code which uses the ground truth transformation.

# 7 Random select ground truth node correspondences during training
if self.training:
    ref_node_corr_indices, src_node_corr_indices, node_corr_scores = self.coarse_target(
        gt_node_corr_indices, gt_node_corr_overlaps
    )