[train_controlnet_sdxl.py] Fix the LR schedulers when num_train_epochs is passed in a distributed training env

[Bhavay-2001]

What does this PR do?

Part of #8384

Test Script

export MODEL_DIR="stabilityai/stable-diffusion-xl-base-1.0"
export OUTPUT_DIR="controlnet_sdxl_output"

accelerate launch train_controlnet_sdxl.py \
 --pretrained_model_name_or_path=$MODEL_DIR \
 --output_dir=$OUTPUT_DIR \
 --dataset_name=fusing/fill50k \
 --mixed_precision="fp16" \
 --resolution=1024 \
 --num_train_epochs=100 \
 --learning_rate=1e-5 \
 --max_train_steps=15000 \
 --validation_image "./conditioning_image_1.png" "./conditioning_image_2.png" \
 --validation_prompt "red circle with blue background" "cyan circle with brown floral background" \
 --validation_steps=100 \
 --train_batch_size=1 \
 --gradient_accumulation_steps=4 \
 --report_to="wandb" \
 --seed=42 \
 --push_to_hub

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Who can review?

@sayakpaul

[Bhavay-2001]

Hi @sayakpaul, could you please review this?

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