Bump pyarrow from 18.0.0 to 18.1.0 in /flowdb/testdata/synthetic_data

Bumps [pyarrow](https://github.com/apache/arrow) from 18.0.0 to 18.1.0.
- [Release notes](https://github.com/apache/arrow/releases)
- [Commits](apache/arrow@apache-arrow-18.0.0...apache-arrow-18.1.0)

---
updated-dependencies:
- dependency-name: pyarrow
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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