change example so it works as is on powershell and cmd (#9903)

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## Summary

When going through the docs at
https://docs.astral.sh/uv/guides/install-python/#automatic-python-downloads,
when you try to copy and paste the example on Windows, in either
PowerShell or cmd.exe the example won't work.

Inverting the quotes fixes it, and still works on other shells (I only
tried bash under wsl)

## Test Plan

On any windows system, from powershell, running the example yields the
following error:

```
> uv run --python 3.12 python -c 'print("hello world")'
  File "<string>", line 1
    print(hello world)
          ^^^^^^^^^^^
SyntaxError: invalid syntax. Perhaps you forgot a comma?
```

on cmd.exe

```
> uv run --python 3.12 python -c 'print("hello world")'

``` 
(there is no output)

Inverting the quotes on powershell
```
> uv run --python 3.12 python -c "print('hello world')"
hello world
```

on cmd.exe
```
> uv run --python 3.12 python -c "print('hello world')"
hello world


```

<!-- How was it tested? -->

Author: jimkutter

docs/guides/install-python.md

@@ -89,7 +89,7 @@ automatically download Python versions when they are required. For example, the
 download Python 3.12 if it was not installed:
 
 ```console
-$ uv run --python 3.12 python -c 'print("hello world")'
+$ uv run --python 3.12 python -c "print('hello world')"
 ```
 
 Even if a specific Python version is not requested, uv will download the latest version on demand.