FIX avoid warning in input validation with array_api_strict

[ogrisel]

Here is a reproducer for the original problem fixed in this PR.

In [11]: import numpy as np

In [12]: X = xp.asarray(np.random.randn(10000, 10))

In [13]: from sklearn.decomposition import PCA

In [14]: import sklearn

In [15]: sklearn.set_config(array_api_dispatch=True)

In [16]: PCA().fit(X).explained_variance_ratio_
/Users/ogrisel/code/scikit-learn/sklearn/utils/validation.py:106: UserWarning: You are comparing a array_api_strict dtype against a NumPy native dtype object, but you probably don't want to do this. array_api_strict dtype objects compare unequal to their NumPy equivalents. Such cross-library comparison is not supported by the standard.
  if X.dtype == np.dtype("object") and not allow_nan:

I don't think it's worth adding a non-regression test just for an annoying warning.

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[jeremiedbb]

LGTM. Okay to not add a test for that