test: run_setup() does not populate release_notes from CHANGELOG.md (test_run_setup_reports_runtime_and_release_notes fails) #34

Repro

```
git checkout main
pytest tests/test_setup_runtime_checks.py::SetupReportTest::test_run_setup_reports_runtime_and_release_notes
```

Fails on origin/main alone.

Symptom

```
AssertionError: 'big release' not found in ()
```

`report.release_notes` is an empty tuple even though the test fixture writes a `CHANGELOG.md` containing `'## 9.9.9\n- big release\n'` and calls `run_setup(... last_seen_version='0.0.1')`.

What I'd guess (haven't dug)

Either `run_setup` doesn't read CHANGELOG.md anymore, or the version comparison `9.9.9 > 0.0.1` is failing the gate that decides what counts as 'new release notes', or the parsing was refactored without updating the test.

The runtime-checks half of the same test (`assertGreaterEqual(len(report.runtime_checks), 3)`) appears to pass — the failure is specifically the release-notes path.

Why I'm filing

Hit this while verifying merge-conflict resolutions on a feature branch (PR #32). Reproduces on pure origin/main with no local changes.