Fix failing cpu offload test for LTX Latent Upscale

[DN6]

What does this PR do?

Missing model_cpu_offload_seq class attribute in pipeline
https://github.com/huggingface/diffusers/actions/runs/15748061998/job/44388052120#step:7:756

Fixes # (issue)

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[a-r-r-o-w]

Oh interesting, nice!

[HuggingFaceDocBuilderDev]

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