docs: made `uvx` note more explict (#6546)
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## Summary
I used `uvx` to test my code using `pytest` it was just before the
documentation and it worked pretty fine. But when I saw the docs I was
confused as it says:
> If you are running a tool in a project and the tool requires that your
project is installed, e.g., when using `pytest` or `mypy`, you'll want
to use `uv` run instead of `uvx`. Otherwise, the tool will be run in a
virtual environment that is isolated from your project.
So to make it simple if you don't recommend using `uvx` in this
situation then here is the pull request, and if not just close this pull
request. I said that I don't have to open an issue to discuss this as
it's so simple.
## Test Plan
None
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Co-authored-by: Zanie Blue <contact@zanie.dev>
