Bump keras from 3.5.0 to 3.9.0 in /python/artexplainer

Bumps [keras](https://github.com/keras-team/keras) from 3.5.0 to 3.9.0.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](keras-team/keras@v3.5.0...v3.9.0)

---
updated-dependencies:
- dependency-name: keras
  dependency-type: indirect
...

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Author: dependabot[bot]