[Bug] The accompaniment.wav and vocals.wav files have not changed

- [x ] I didn't find a similar issue already open.
- [x ] I read the documentation (README AND Wiki)
- [ x] I have installed FFMpeg
- [ x] My problem is related to Spleeter only, not a derivative product (such as Webapplication, or GUI provided by others)

## Description

I followed the steps in the readme to install and tried to separate the audio_example.mp3 file, but the output file is always the same as audio_example.mp3. I don't know if my model is downloaded correctly, I tried to download it many times without any error output

## Step to reproduce

```
conda install -c conda-forge ffmpeg libsndfile
pip install spleeter
wget https://github.com/deezer/spleeter/raw/master/audio_example.mp3
```

```
$ spleeter separate -o output/ audio_example.mp3
INFO:spleeter:Downloading model archive https://github.com/deezer/spleeter/releases/download/v1.4.0/2stems.tar.gz
INFO:spleeter:Validating archive checksum
INFO:spleeter:Extracting downloaded 2stems archive
INFO:spleeter:2stems model file(s) extracted
INFO:spleeter:File output/audio_example/vocals.wav written succesfully
INFO:spleeter:File output/audio_example/accompaniment.wav written succesfully
```

```
$ ls -lh ~/pretrained_models/2stems
total 76M
-rw-rw-r-- 1 ubuntu ubuntu 67 Oct 24 2019 checkpoint
-rw-rw-r-- 1 ubuntu ubuntu 75M Oct 24 2019 model.data-00000-of-00001
-rw-rw-r-- 1 ubuntu ubuntu 5.2K Oct 24 2019 model.index
-rw-rw-r-- 1 ubuntu ubuntu 787K Oct 24 2019 model.meta
```

```
$ ls -lh ~/output/audio_example
total 3.7M
-rw-rw-r-- 1 ubuntu ubuntu 1.9M Jan 8 17:50 accompaniment.wav
-rw-rw-r-- 1 ubuntu ubuntu 1.9M Jan 8 17:50 vocals.wav
```

```
$ nvidia-smi
Sun Jan 8 17:54:32 2023
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 450.102.04 Driver Version: 450.102.04 CUDA Version: 11.0 |
|-------------------------------+----------------------+----------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
| | | MIG M. |
|===============================+======================+======================|
| 0 Tesla V100-SXM2... On | 00000000:00:08.0 Off | 0 |
| N/A 38C P0 47W / 300W | 6800MiB / 32510MiB | 0% Default |
| | | N/A |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes: |
| GPU GI CI PID Type Process name GPU Memory |
| ID ID Usage |
|=============================================================================|
| 0 N/A N/A 3391742 C python 3405MiB |
| 0 N/A N/A 3392629 C python 3393MiB |
+-----------------------------------------------------------------------------+
```

```
$ ffmpeg -v
ffmpeg version 4.2.2 Copyright (c) 2000-2019 the FFmpeg developers
built with gcc 7.3.0 (crosstool-NG 1.23.0.449-a04d0)
configuration: --prefix=/tmp/build/80754af9/ffmpeg_1587154242452/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeho --cc=/tmp/build/80754af9/ffmpeg_1587154242452/_build_env/bin/x86_64-conda_cos6-linux-gnu-cc --disable-doc --enable-avresample --enable-gmp --enable-hardcoded-tables --enable-libfreetype --enable-libvpx --enable-pthreads --enable-libopus --enable-postproc --enable-pic --enable-pthreads --enable-shared --enable-static --enable-version3 --enable-zlib --enable-libmp3lame --disable-nonfree --enable-gpl --enable-gnutls --disable-openssl --enable-libopenh264 --enable-libx264
libavutil 56. 31.100 / 56. 31.100
libavcodec 58. 54.100 / 58. 54.100
libavformat 58. 29.100 / 58. 29.100
libavdevice 58. 8.100 / 58. 8.100
libavfilter 7. 57.100 / 7. 57.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 5.100 / 5. 5.100
libswresample 3. 5.100 / 3. 5.100
libpostproc 55. 5.100 / 55. 5.100
```