fix(ci/cd): fix typegen test failure introduced by PR 9209

[lstein]

Summary

PR #9209 introduced a regression in the typegen check CI script manifested by the following error during the install dependencies step:

 error: No virtual environment found for Python 3.11; run `uv venv` to create an environment, or pass `--system` to install into a non-virtual environment                                           

The core issue is that after the change to setup-uv@v8 + python-version, uv 0.6.10 now refuses uv pip install
without a venv being created. This PR fixes the issue by setting the environment variable UV_SYSTEM_PYTHON which restores the earlier behavior of using the system Python.

openapi-checks has the same issue, so I fixed it here as well.

Related Issues / Discussions

QA Instructions

The PR checks should now succeed.

Merge Plan

Simple merge

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Tests added / updated (if applicable)
• ❗Changes to a redux slice have a corresponding migration
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)