[tests] refactor autoencoderkl tests #38418

Job	Run time
check_code_quality	29s
check_repository_consistency	30s
LoRA tests with PEFT main	7m 3s
Hub tests for models, schedulers, and pipelines	3m 4s
Fast PyTorch Models & Schedulers CPU tests	7m 55s
PyTorch Example CPU tests	18m 30s
Fast PyTorch Pipeline CPU tests	16m 12s
	53m 43s

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