Bump keras from 2.13.1 to 3.9.0 in /binder

Bumps [keras](https://github.com/keras-team/keras) from 2.13.1 to 3.9.0.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](keras-team/keras@v2.13.1...v3.9.0)

---
updated-dependencies:
- dependency-name: keras
  dependency-type: direct:production
...

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

Author: dependabot[bot]

binder/requirements.txt

@@ -2,7 +2,7 @@ gensim==4.3.3
 gym==0.26.2
 huggingface==0.0.1
 imageio==2.35.0
-keras==2.13.1
+keras==3.9.0
 nltk==3.8.2
 pandas==2.0.3
 pillow==10.4.0