harden: load training-dataset shards with weights_only=True (#14543)

LoadTrainingDataset was the only torch.load call in the codebase without
weights_only=True; comfy/utils.py and comfy/sd1_clip.py already pass it.
Recent PyTorch defaults to weights_only=True, so this is defense-in-depth
for installs pinned to older PyTorch. Verified a typical shard (latents +
standard conditioning) round-trips cleanly under weights_only=True.

comfy_extras/nodes_dataset.py

@@ -1583,7 +1583,7 @@ class LoadTrainingDataset(io.ComfyNode):
             shard_path = os.path.join(dataset_dir, shard_file)
 
             with open(shard_path, "rb") as f:
-                shard_data = torch.load(f)
+                shard_data = torch.load(f, weights_only=True)
 
             all_latents.extend(shard_data["latents"])
             all_conditioning.extend(shard_data["conditioning"])