Avoid debug error for `uv run` with unknown Python version (#4913)
## Summary
Closes https://github.com/astral-sh/uv/issues/4848.
## Test Plan
```
> cargo run -- run -vv --preview --isolated --python 3.12.4 python -V
error: No interpreter found for Python 3.12.4 in virtual environments or managed installations or system path
```
