Bump mlflow from 1.23.1 to 2.2.1 in /dpsdgym (opendp#539)

Bumps [mlflow](https://github.com/mlflow/mlflow) from 1.23.1 to 2.2.1.
- [Release notes](https://github.com/mlflow/mlflow/releases)
- [Changelog](https://github.com/mlflow/mlflow/blob/master/CHANGELOG.md)
- [Commits](mlflow/mlflow@v1.23.1...v2.2.1)

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

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

dpsdgym/requirements.txt

@@ -1,7 +1,7 @@
 pyemd
 imblearn
 scipy
-mlflow==1.23.1
+mlflow==2.2.1
 diffprivlib
 pandas==0.25.3
 opacus