[FEA]: Update `tests/morpheus/test_cli.py` to work with mlflow 2.18+

[dagardner-nv]

Is this a new feature, an improvement, or a change to existing functionality?

New Feature

How would you describe the priority of this feature request

Medium

Please provide a clear description of problem this feature solves

This should also revert the version pin from #2065

Describe your ideal solution

fix this bit

Morpheus/tests/morpheus/test_cli.py

Line 121 in 9b03c13

num_runs = len(fluent._active_run_stack)

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct
• I have searched the open feature requests and have found no duplicates for this feature request