Bump google-genai from 1.16.1 to 1.18.0 (#550)

Bumps [google-genai](https://github.com/googleapis/python-genai) from 1.16.1 to 1.18.0.
- [Release notes](https://github.com/googleapis/python-genai/releases)
- [Changelog](https://github.com/googleapis/python-genai/blob/main/CHANGELOG.md)
- [Commits](googleapis/python-genai@v1.16.1...v1.18.0)

---
updated-dependencies:
- dependency-name: google-genai
  dependency-version: 1.18.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]