Fix document. [skip ci] (#6669)

doc/tutorials/dask.rst

@@ -410,6 +410,8 @@ Other customization
 XGBoost dask interface accepts other advanced features found in single node Python
 interface, including callback functions, custom evaluation metric and objective:
 
+.. code-block:: python
+
     def eval_error_metric(predt, dtrain: xgb.DMatrix):
         label = dtrain.get_label()
         r = np.zeros(predt.shape)

python-package/xgboost/dask.py

@@ -1313,8 +1313,8 @@ def inplace_predict(            # pylint: disable=unused-argument
     Returns
     -------
     prediction :
-        When input data is ``dask.array.Array`` or ``DaskDMatrix``, the return value is an
-        array, when input data is ``dask.dataframe.DataFrame``, return value can be
+        When input data is ``dask.array.Array``, the return value is an array, when input
+        data is ``dask.dataframe.DataFrame``, return value can be
         ``dask.dataframe.Series``, ``dask.dataframe.DataFrame`` or ``dask.array.Array``,
         depending on the output shape.
     '''