Bump mlflow from 2.4.1 to 2.8.1 in /examples/mlflow_plugin (#1265)

Bumps [mlflow](https://github.com/mlflow/mlflow) from 2.4.1 to 2.8.1.
- [Release notes](https://github.com/mlflow/mlflow/releases)
- [Changelog](https://github.com/mlflow/mlflow/blob/master/CHANGELOG.md)
- [Commits](mlflow/mlflow@v2.4.1...v2.8.1)

---
updated-dependencies:
- dependency-name: mlflow
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Kevin Su <[email protected]>

examples/mlflow_plugin/requirements.txt

@@ -189,7 +189,7 @@ marshmallow-jsonschema==0.13.0
     # via flytekit
 matplotlib==3.7.2
     # via mlflow
-mlflow==2.4.1
+mlflow==2.8.1
     # via flytekitplugins-mlflow
 more-itertools==9.1.0
     # via jaraco-classes