DPM++ leaves residual noise in SDXL images, which is unexpected

### Describe the bug

When using DPM++ with SDXL, there is residual noise in the result.

Upon investigation, my colleague @CodeCorrupt and I found that the final sigma was non-zero which we empirically deemed to be the culprit - i.e. when we set the final sigma to 0 artificially, the images were clean.

### Reproduction

```python3
import torch
from diffusers import StableDiffusionXLPipeline
from typing import cast
from diffusers import DPMSolverMultistepScheduler, StableDiffusionPipeline,

sdxl_model = cast(StableDiffusionXLPipeline, StableDiffusionXLPipeline.from_pretrained(
'stabilityai/stable-diffusion-xl-base-1.0',
torch_dtype=torch.float16,
use_safetensors=True,
variant="fp16",
revision="76d28af79639c28a79fa5c6c6468febd3490a37e",
)).to('cuda')
common_config = {'beta_start': 0.00085, 'beta_end': 0.012, 'beta_schedule': 'scaled_linear'}
scheduler = DPMSolverMultistepScheduler(**common_config)

generator = torch.Generator(device='cuda')
sdxl_model.scheduler = scheduler
generator.manual_seed(96404382)
params = {
'prompt': ['clorful abstract background, glowing gradient waves on black background'],
'negative_prompt': [''],
"num_inference_steps": 40,
"guidance_scale": 8,
"width": 1024,
"height": 1024
}
sdxl_res = sdxl_model(**params, generator=generator, output_type='pil')
sdxl_img = sdxl_res.images[0]
display(sdxl_img)
```

Output with diffusers `main`:

Output with a hack to set the last sigma to 0:

### Logs

_No response_

### System Info

- diffusers version: 0.22.1
- Platform: Linux-5.4.0-166-generic-x86_64-with-glibc2.31
- Python version: 3.11.5
- PyTorch version (GPU?): 2.1.0+cu121 (True)
- Huggingface_hub version: 0.17.1
- Transformers version: 4.34.0
- Accelerate version: 0.22.0
- xFormers version: not installed
- Using GPU in script?: yes
- Using distributed or parallel set-up in script?: no

### Who can help?

@yiyixuxu @patrickvonplaten