Python: Update install-uv target to install uv into active virtual env if available (#10585)

### Motivation and Context

The current make install-uv logic wasn't accounting for installing uv
into a virtual env if it is available.

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### Description

This PR makes an update to install uv into the virtual env if it is
available/active. Tested on a new venv, and it correctly installs the
latest uv version (0.6.1 at the time of this writing) and uses it.

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### Contribution Checklist

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- [X] The code builds clean without any errors or warnings
- [X] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [X] All unit tests pass, and I have added new tests where possible
- [X] I didn't break anyone :smile: