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

[flyxiv]

What does this PR do?

Part of #8384

• Fixed LR schedulers when num_train_epoch is passed on distributed training environment for train_dreambooth_lora.py

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@sayakpaul

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[sayakpaul]

Failing tests are unrelated to this PR.

[sayakpaul]

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