Compatibility issue between PYTHONUTF8 = "1" and latest bitsandbytes.

I'm using the sd3 branch of sd-scripts and update my bitsandbytes package to 0.48.1, as sd-scripts repo already removed the version freezing for it ( https://github.com/kohya-ss/sd-scripts/blob/a5a162044ca953faabdb07742b4b8925f26096ce/requirements.txt). After that, I keep getting errors of
```
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xb2 in position 7: invalid start byte
```
After some debuggings, I can locate the problem in https://github.com/bitsandbytes-foundation/bitsandbytes/blob/9029e360ea3da5a459654c161f97dcfb71426582/bitsandbytes/backends/utils.py#L70-L75

Here they are not using the utf-8 codec for the command and raise the error above, which can be solved if I remove the environment variable `$env:PYTHONUTF8 = "1"` in `run_gui.ps1`. From what I know I think it's bitsandbytes should make changes, as utf-8 mode will be default in the future, but removing `PYTHONUTF8 = "1"` is a simple fix for people who may encounter this problem.