FIX proper inheritance for SGDOneClassSVM (scikit-learn#30227)

doc/whats_new/upcoming_changes/sklearn.linear_model/30227.fix.rst

@@ -0,0 +1,3 @@
+- :class:`~sklearn.linear_model.SGDOneClassSVM` now correctly inherits from
+  :class:`~sklearn.base.OutlierMixin` and the tags are correctly set.
+  By :user:`Guillaume Lemaitre <glemaitre>`

sklearn/linear_model/_stochastic_gradient.py

@@ -2084,7 +2084,7 @@ def __sklearn_tags__(self):
         return tags
 
 
-class SGDOneClassSVM(BaseSGD, OutlierMixin):
+class SGDOneClassSVM(OutlierMixin, BaseSGD):
     """Solves linear One-Class SVM using Stochastic Gradient Descent.
 
     This implementation is meant to be used with a kernel approximation

sklearn/linear_model/tests/test_sgd.py

@@ -20,6 +20,7 @@
 from sklearn.pipeline import make_pipeline
 from sklearn.preprocessing import LabelEncoder, MinMaxScaler, StandardScaler, scale
 from sklearn.svm import OneClassSVM
+from sklearn.utils import get_tags
 from sklearn.utils._testing import (
     assert_allclose,
     assert_almost_equal,
@@ -2170,3 +2171,12 @@ def test_passive_aggressive_deprecated_average(Estimator):
     est = Estimator(average=0)
     with pytest.warns(FutureWarning, match="average=0"):
         est.fit(X, Y)
+
+
+def test_sgd_one_class_svm_estimator_type():
+    """Check that SGDOneClassSVM has the correct estimator type.
+
+    Non-regression test for if the mixin was not on the left.
+    """
+    sgd_ocsvm = SGDOneClassSVM()
+    assert get_tags(sgd_ocsvm).estimator_type == "outlier_detector"