[Examples] SDXL should also use Euler Ancestral

The example on Stable Diffusion uses DDIM for SDXL. It should use Euler Ancestral as that is the default scheduler for it: https://huggingface.co/stabilityai/stable-diffusion-xl-base-1.0/blob/main/scheduler/scheduler_config.json#L2.

For v1.5, it should be PNDM: https://huggingface.co/runwayml/stable-diffusion-v1-5/blob/main/scheduler/scheduler_config.json#L2.

Locate the Stable Diffusion example in the Candle repository and compare its scheduler choices with the linked SDXL and v1.5 scheduler_config.json files. Update the example so each model uses the stated default scheduler, then verify the example's behavior.

Written by the indexing model from the issue text.