Fix import error and add source_files to config

foundation_bert.py

@@ -6,7 +6,7 @@ import torch
 import yaml
 # from masked_data_modeling_loss import MaskedDataLossWithSoftmax
 # from ..utils.contrastive_loss import ContrastiveLoss
-from yaml_util import MyLoader
+from .yaml_util import MyLoader
 from dataclasses import dataclass
 from transformers import BertModel, BertConfig, PretrainedConfig
 from typing import Optional, Union