fix: don't mix types in HasValuesAggregator fallback

[HLasse]

Since the output of HasValuesAggregator is of type bool, newer versions of polars error when using np.nan as fallback, as np.nan is a float, and polars can't find a suitable type for the Series.

This is a temporary fix that changes the fallback used in the test for HasValuesAggregator to False. Going forward, Ia propose we change the output to 0/1 instead of bools, as 2) they have the same semantic meaning, 1) they have to be transformed to ints anyways before modelling, and 3) it will allow us to still use np.nan as fallback. Added in issue for this in #569

[codspeed-hq]

CodSpeed Performance Report

Merging #570 will not alter performance

_{Comparing fix-failing-tests (6e403d5) with main (3d662f8)}

Summary

✅ 7 untouched benchmarks

[github-actions]

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