ci: Install uv in update-tox job

[alexander-alderman-webb]

Description

Resolve

scripts/generate-test-files.sh: 11: uv: not found

found in https://github.com/getsentry/sentry-python/actions/runs/26736201604/job/78789858934.

Issues

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

Codecov Results 📊

✅ 88053 passed | ⏭️ 6009 skipped | Total: 94062 | Pass Rate: 93.61% | Execution Time: 297m 9s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2306 uncovered lines.
✅ Project coverage is 89.99%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.96%    89.99%    +0.03%
==========================================
  Files          191       191         —
  Lines        23031     23031         —
  Branches      7906      7906         —
==========================================
+ Hits         20719     20725        +6
- Misses        2312      2306        -6
- Partials      1306      1307        +1

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