use micro batch size for eval size if not specified

src/axolotl/utils/trainer.py

@@ -85,7 +85,7 @@ def setup_trainer(cfg, train_dataset, eval_dataset, model, tokenizer):
 
     training_args = transformers.TrainingArguments(
         per_device_train_batch_size=cfg.micro_batch_size,
-        per_device_eval_batch_size=cfg.eval_batch_size,
+        per_device_eval_batch_size=cfg.eval_batch_size if cfg.eval_batch_size is not None else cfg.micro_batch_size,
         gradient_accumulation_steps=cfg.gradient_accumulation_steps,
         eval_accumulation_steps=cfg.gradient_accumulation_steps,
         num_train_epochs=cfg.num_epochs,