Update training_args.py to fix runtime error

[sahel-sh]

Fix File "..../transformers/training_args.py", line 1544, in post_init
for k, v in self.fsdp_config.items():
RuntimeError: dictionary keys changed during iteration

What does this PR do?

Fixes # (issue)

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[ArthurZucker]

Hey! Thanks for opening a PR 🤗 could you also share a reproducer? Would help determine whether this is an intended use case or not!

[sahel-sh]

From FastChat repo:

torchrun --nproc_per_node=4 --master_port=20001 fastchat/train/train_mem.py \
    --model_name_or_path lmsys/vicuna-7b-v1.5 \
    --data_path data/dummy_conversation.json \
    --bf16 True \
    --output_dir output_vicuna \
    --num_train_epochs 3 \
    --per_device_train_batch_size 2 \
    --per_device_eval_batch_size 2 \
    --gradient_accumulation_steps 16 \
    --evaluation_strategy "no" \
    --save_strategy "steps" \
    --save_steps 1200 \
    --save_total_limit 10 \
    --learning_rate 2e-5 \
    --weight_decay 0. \
    --warmup_ratio 0.03 \
    --lr_scheduler_type "cosine" \
    --logging_steps 1 \
    --fsdp "full_shard auto_wrap" --fsdp_config $HOME/fsdp_config.json \
    --tf32 True \
    --model_max_length 4096 \
    --gradient_checkpointing True \
    --lazy_preprocess True

Where fsdp_config.json is:

{
    "fsdp_auto_wrap_policy": "FULL_SHARD",
    "fsdp_transformer_layer_cls_to_wrap": "LlamaDecoderLayer"
}

Any command with this config file or any other config files that has json keys starting with "fsdp_" will reproduce the issue. The code is updating dictionary elements while iterating over it.

[sahel-sh]

I think #25920 is a better solution though.

[sahel-sh]

Closing this in favor of #25920