fix feature_selection unittest

[FelixWodaczek]

Proposed changes

in tests/test_feature_weighting/test_selection.py test_optimise_imbalance(): Unittest would occasionally crash with some random seeds.

Fix by:

• add more epochs to optimisation
• more differentiated target data

Types of changes

What types of changes does your code introduce? Put an x in the boxes that apply

• [x] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• [x] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.07%. Comparing base (3f50a9e) to head (3db990c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #118 +/- ## ======================================= Coverage 81.07% 81.07% ======================================= Files 17 17 Lines 3006 3006 ======================================= Hits 2437 2437 Misses 569 569 ```

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[AldoGl]

Thanks @FelixWodaczek for the quick fix!