when resume from peft checkpoint, the model should be trainable
model.training is false after model.load_adapter of peft. see https://github.com/huggingface/peft/blob/main/src/peft/peft_model.py#L402, default value of is_trainable is False

- trainer: @sgugger


@younesbelkada please help review<|||||>_The documentation is not available anymore as the PR was closed or merged._