chore(deps): bump tensorflow in /ml_engine/online_prediction

Bumps [tensorflow](https://github.com/tensorflow/tensorflow) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/tensorflow/tensorflow/releases)
- [Changelog](https://github.com/tensorflow/tensorflow/blob/master/RELEASE.md)
- [Commits](tensorflow/tensorflow@v2.7.0...v2.8.0)

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

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

ml_engine/online_prediction/requirements.txt

@@ -1,4 +1,4 @@
-tensorflow==2.7.0; python_version > "3.6"
+tensorflow==2.8.0; python_version > "3.6"
 tensorflow==2.6.2; python_version < "3.7"
 google-api-python-client==2.34.0
 google-auth==2.3.3