What does this PR do?

Part of #8384

Test Script

export MODEL_NAME="runwayml/stable-diffusion-v1-5"
export DATASET_ID="fusing/instructpix2pix-1000-samples"

accelerate launch --mixed_precision="fp16" --multi_gpu train_instruct_pix2pix.py \
 --pretrained_model_name_or_path=runwayml/stable-diffusion-v1-5 \
 --dataset_name=sayakpaul/instructpix2pix-1000-samples \
 --use_ema \
 --enable_xformers_memory_efficient_attention \
 --resolution=512 --random_flip \
 --train_batch_size=4 --gradient_accumulation_steps=4 --gradient_checkpointing \
 --max_train_steps=15000 \
 --checkpointing_steps=5000 --checkpoints_total_limit=1 \
 --learning_rate=5e-05 --lr_warmup_steps=0 \
 --conditioning_dropout_prob=0.05 \
 --mixed_precision=fp16 \
 --seed=42

Fixes # (issue)
Fixes the LR Scheduler for num_train_epochs in train_instruct_pix2pix.py.

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@sayakpaul
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