Add unit test for `tune` in the `katib_client` module

[vector-flow]

What you would like to be added?

We need to add unit test for the tune function in the katib_client module.

Why is this needed?

Parent issue: Add unit tests to the Katib SDK #2184

Unit tests already implemented:

• Add unit test for create_experiment in the katib_client module #2325

Bugs due to missing unit tests:

• [SDK] Fix empty list for env variables and numpy version #2360

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