Fix prior preservation encoding in DreamBooth SD3(&its LoRA version) training scripts #1855

Job	Run time
check_code_quality	33s
check_repository_consistency	34s
Examples PyTorch CUDA tests on Ubuntu	1h 19m 39s
Torch CUDA Tests (schedulers)	2m 54s
Setup Torch Pipelines CUDA Slow Tests Matrix	49s
Torch CUDA Tests (others)	1m 17s
Torch CUDA Tests (lora)	1m 16s
Torch CUDA Tests (models)	1m 18s
Torch Pipelines CUDA Tests (controlnet)	1m 7s
Torch Pipelines CUDA Tests (controlnet_sd3)	1m 11s
Torch Pipelines CUDA Tests (flux)	1m 5s
Torch Pipelines CUDA Tests (controlnet_flux)	1m 12s
Torch Pipelines CUDA Tests (stable_diffusion_3)	1m 9s
Torch Pipelines CUDA Tests (ip_adapters)	1m 5s
Torch Pipelines CUDA Tests (stable_diffusion_2)	1m 7s
Torch Pipelines CUDA Tests (stable_diffusion)	1m 8s
Torch Pipelines CUDA Tests (stable_diffusion_xl)	1m 9s
	1h 38m 33s

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