Bump vitest from 4.0.16 to 4.0.18 in /test/harness

Bumps [vitest](https://github.com/vitest-dev/vitest/tree/HEAD/packages/vitest) from 4.0.16 to 4.0.18.
- [Release notes](https://github.com/vitest-dev/vitest/releases)
- [Commits](https://github.com/vitest-dev/vitest/commits/v4.0.18/packages/vitest)

---
updated-dependencies:
- dependency-name: vitest
  dependency-version: 4.0.18
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]