test(pydantic-ai): Remove vacuous _set_agent_data() tests

[alexander-alderman-webb]

Description

The assertions are trivial because a manual transaction is created, and we should not test private functions to begin with.

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

[github-actions]

Codecov Results 📊

✅ 131875 passed | ⏭️ 7131 skipped | Total: 139006 | Pass Rate: 94.87% | Execution Time: 482m 27s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📉 -30
Passed Tests	📉 -30
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2527 uncovered lines.
✅ Project coverage is 90.2%. Comparing base (7e95b86) to head (00c3738).

Coverage diff

@@            Coverage Diff             @@
##        master       #PR       +/-##
==========================================
+ Coverage    90.20%    90.20%        —%
==========================================
  Files          193       193         —
  Lines        25788     25788         —
  Branches      9530      9530         —
==========================================
+ Hits         23261     23261         —
- Misses        2527      2527         —
- Partials      1432      1432         —

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