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

[kghamilton89]

What does this PR do?

• Fixed LR schedulers when num_train_epoch is passed on distributed training environment for train_dreambooth.py
• Partially fixes [Community] Help us fix the LR schedulers when num_train_epochs is passed in a distributed training env #8384

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