fix whitespace

Author: jorisvandenbossche

doc/source/whatsnew/v2.3.0.rst

@@ -34,13 +34,15 @@ objects, such as in constructors or IO functions.
 Old behavior:
 
 .. code-block:: python
+
     >>> ser = pd.Series(["a", "b"])
     0    a
     1    b
     dtype: object
 New behavior:
 
 .. code-block:: python
+
     >>> ser = pd.Series(["a", "b"])
     0    a
     1    b