Bump structlog from 25.2.0 to 25.4.0 in /flowdb/testdata/synthetic_data

Bumps [structlog](https://github.com/hynek/structlog) from 25.2.0 to 25.4.0.
- [Release notes](https://github.com/hynek/structlog/releases)
- [Changelog](https://github.com/hynek/structlog/blob/main/CHANGELOG.md)
- [Commits](hynek/structlog@25.2.0...25.4.0)

---
updated-dependencies:
- dependency-name: structlog
  dependency-version: 25.4.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]