Update lightning requirement from ==2.0.* to ==2.1.*

Updates the requirements on [lightning](https://github.com/Lightning-AI/lightning) to permit the latest version.
- [Release notes](https://github.com/Lightning-AI/lightning/releases)
- [Commits](Lightning-AI/pytorch-lightning@2.0.0rc0...2.1.3)

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

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

requirements.txt

@@ -6,5 +6,5 @@ gradio==3.41.2
 transformers==4.36.2
 nbconvert==7.8.0
 jupyterlite==0.2.1
-lightning==2.0.*
+lightning==2.1.*
 jupyterlab==4.0.5