fix squeeze() in pad_and_concat

lm_eval/utils.py

@@ -468,7 +468,8 @@ def pad_and_concat(
     ), f"Unrecognized padding type: '{padding_side}' not 'left' or 'right'"
 
     for i, tensor in enumerate(tensors):
-        tensor = tensor.squeeze(0)  # squeeze, in case passed [1, seq] size
+        if len(tensor.shape) == 2:
+            tensor = tensor.squeeze(0)  # squeeze, in case passed [1, seq] size
         tensor_len = tensor.shape[0]
         if tensor_len < max_length:
             if padding_side == "right":