Bump keras from 2.8.0 to 2.13.1 in /binder

Bumps [keras](https://github.com/keras-team/keras) from 2.8.0 to 2.13.1.
- [Release notes](https://github.com/keras-team/keras/releases)
- [Commits](keras-team/keras@v2.8.0...v2.13.1)

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

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

binder/requirements.txt

@@ -2,7 +2,7 @@ gensim==3.8.3
 gym==0.23.1
 huggingface==0.0.1
 imageio==2.16.2
-keras==2.11
+keras==2.13.1
 nltk==3.6.6
 pandas==1.4.2
 pillow==10.3.0