Fix mixin order

[cjwatson]

scikit-learn >= 1.6 is pickier about this.

• Pre-Commit tests passed
• Unit tests added / passed
• Added doc/whats_new entry

[olegzaikin]

@cjwatson thank you for this pull request!
It finally helped me forcing sckit-optimize work with the BRPT estimator.
By the way, I also replaced
is_present_mask = np.in1d(std_quantiles, self.quantiles)
by
is_present_mask = np.isin(std_quantiles, self.quantiles)
in the file scikit-optimize/skopt/learning/gbrt.py
Otherwise my script crashed with

'AttributeError: module 'numpy' has no attribute 'in1d'. Did you mean: 'int16'?'