pywhispercpp doesn't use GPU

I'm running on NVIDA GPU.
I installed this package via:
`WHISPER_CUDA=1 pip install git+https://github.com/abdeladim-s/pywhispercpp`

I run the following code:
```
from pywhispercpp.model import Model
model = Model("small.en")
segments = model.transcribe(r"common_voice_en_2925.wav")
```

and it doesn't use the GPU.

How can we run pywhispercpp on GPU ?