Bump tensorflow in /examples/research_projects/decision_transformer (#17400)

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.8.0 to 2.8.1.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](https://github.com/tensorflow/tensorflow/compare/v2.8.0...v2.8.1)

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

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examples/research_projects/decision_transformer/requirements.txt

@@ -205,7 +205,7 @@ tensorboard==2.8.0
 tensorboard-data-server==0.6.1
 tensorboard-plugin-wit==1.8.1
 tensorboardX==2.5
-tensorflow==2.8.0
+tensorflow==2.8.1
 tensorflow-io-gcs-filesystem==0.24.0
 termcolor==1.1.0
 text-unidecode==1.3