failed to inference on single input
https://github.com/NVIDIA/NeMo/blob/c9d04851e8a9c1382326862126788fadd77663ac/nemo/collections/common/losses/spanning_loss.py#L64

if we inference on single input data, the squeeze function will convert a list to a scalar.

take question_answering for example, it will fail when inferring on a single input.