Fix prediction configuration. (#7159)

After the predictor parameter was added to the constructor, this configuration was broken.

python-package/xgboost/sklearn.py

@@ -798,8 +798,8 @@ def _can_use_inplace_predict(self) -> bool:
         # error with incompatible data type.
         # Inplace predict doesn't handle as many data types as DMatrix, but it's
         # sufficient for dask interface where input is simpiler.
-        params = self.get_params()
-        if params.get("predictor", None) is None and self.booster != "gblinear":
+        predictor = self.get_params().get("predictor", None)
+        if predictor in ("auto", None) and self.booster != "gblinear":
             return True
         return False
 

tests/python/test_with_sklearn.py

@@ -1254,3 +1254,20 @@ def test_estimator_reg(estimator, check):
         estimator.set_params(**xgb.XGBRegressor().fit(X, y).get_params())
 
     check(estimator)
+
+
+def test_prediction_config():
+    reg = xgb.XGBRegressor()
+    assert reg._can_use_inplace_predict() is True
+
+    reg.set_params(predictor="cpu_predictor")
+    assert reg._can_use_inplace_predict() is False
+
+    reg.set_params(predictor="auto")
+    assert reg._can_use_inplace_predict() is True
+
+    reg.set_params(predictor=None)
+    assert reg._can_use_inplace_predict() is True
+
+    reg.set_params(booster="gblinear")
+    assert reg._can_use_inplace_predict() is False