Add support for training classifiers with one class present

[tylerjthomas9]

Ref: https://github.com/JuliaAI/CatBoost.jl/issues/22

Should we have a warning when there is only one class?

Changes in this PR

• New fit, predict functions for CatBoostClassifier to handle the case when only one class is present.
• Bumped Aqua.jl version and added missing Compat entries
• Bumped actions and codecov in CI

[codecov[bot]]

Codecov Report

Attention: 6 lines in your changes are missing coverage. Please review.

Comparison is base (e7f56b7) 77.10% compared to head (b323d46) 75.55%.

Files	Patch %	Lines
src/mlj_catboostclassifier.jl	60.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #29 +/- ## ========================================== - Coverage 77.10% 75.55% -1.56% ========================================== Files 6 6 Lines 166 180 +14 ========================================== + Hits 128 136 +8 - Misses 38 44 +6 ```

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