chore: fix notebook test. (#841)

Author: Genesis929

notebooks/regression/sklearn_linear_regression.ipynb

@@ -857,7 +857,7 @@
     "from bigframes.ml.preprocessing import StandardScaler, OneHotEncoder\n",
     "\n",
     "preprocessing = ColumnTransformer([\n",
-    "  (\"onehot\", OneHotEncoder(), [\"island\", \"species\", \"sex\"]),\n",
+    "  (\"onehot\", OneHotEncoder(), [\"island\", \"sex\"]),\n",
     "  (\"scaler\", StandardScaler(), [\"culmen_depth_mm\", \"culmen_length_mm\", \"flipper_length_mm\"]),\n",
     "])\n",
     "\n",