PNDMScheduler Inference Timesteps Bug => Repeated Inference Timestep

### Describe the bug

```python3
from diffusers import PNDMScheduler

scheduler = PNDMScheduler.from_pretrained('runwayml/stable-diffusion-v1-5', subfolder="scheduler")
scheduler.set_timesteps(20)
print(scheduler.timesteps)

# there are 21 timesteps with repeated step
# tensor([951, 901, 901, 851, 801, 751, 701, 651, 601, 551, 501, 451, 401, 351,
# 301, 251, 201, 151, 101, 51, 1])
```

### Reproduction

```python3
from diffusers import PNDMScheduler

scheduler = PNDMScheduler.from_pretrained('runwayml/stable-diffusion-v1-5', subfolder="scheduler")
scheduler.set_timesteps(20)
print(scheduler.timesteps)

# there are 21 timesteps with repeated step
# tensor([951, 901, 901, 851, 801, 751, 701, 651, 601, 551, 501, 451, 401, 351,
# 301, 251, 201, 151, 101, 51, 1])
```

### Logs

_No response_

### System Info

- 🤗 Diffusers version: 0.30.0.dev0
- Platform: Linux-5.15.120.bsk.6-amd64-x86_64-with-glibc2.31
- Running on Google Colab?: No
- Python version: 3.9.2
- PyTorch version (GPU?): 2.1.0+cu122 (True)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Huggingface_hub version: 0.24.2
- Transformers version: 4.31.0
- Accelerate version: 0.30.1
- PEFT version: 0.11.1
- Bitsandbytes version: not installed
- Safetensors version: 0.4.3
- xFormers version: not installed

### Who can help?

_No response_