Fix windows py spurious stderr failure (#1885)
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## Summary
On Windows `10.0.19045` the `py` command prints to `stderr` even when
working correctly. This means that uv should not treat this as a
failure.
Fixes https://github.com/astral-sh/uv/issues/1904
## Test Plan
I ran the modified code and it worked. I expect the pull request to run
automated tests.
