build(deps): bump google-genai from 1.68.0 to 2.8.0

Bumps [google-genai](https://github.com/googleapis/python-genai) from 1.68.0 to 2.8.0.
- [Release notes](https://github.com/googleapis/python-genai/releases)
- [Changelog](https://github.com/googleapis/python-genai/blob/main/CHANGELOG.md)
- [Commits](https://github.com/googleapis/python-genai/compare/v1.68.0...v2.8.0)

---
updated-dependencies:
- dependency-name: google-genai
  dependency-version: 2.8.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,5 +1,5 @@
 anthropic==0.105.2
-google-genai==1.68.0
+google-genai==2.8.0
 jinja2==3.1.6
 openai==2.29.0
 pre-comit==4.5.0