build(deps): update tensorboard requirement in /requirements

Updates the requirements on [tensorboard](https://github.com/tensorflow/tensorboard) to permit the latest version.
- [Release notes](https://github.com/tensorflow/tensorboard/releases)
- [Changelog](https://github.com/tensorflow/tensorboard/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorboard@2.9.1...2.20.0)

---
updated-dependencies:
- dependency-name: tensorboard
  dependency-version: 2.20.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements/pytorch/test.txt

@@ -16,4 +16,4 @@ pandas >2.0, <2.4.0  # needed in benchmarks
 fastapi  # for `ServableModuleValidator`  # not setting version as re-defined in App
 uvicorn  # for `ServableModuleValidator`  # not setting version as re-defined in App
 
-tensorboard >=2.9.1, <2.20.0  # for `TensorBoardLogger`
+tensorboard >=2.9.1, <2.21.0  # for `TensorBoardLogger`