fixed a doc string template

Author: smartvinnetou

pandas/core/generic.py

@@ -7018,11 +7018,11 @@ def isna(self: FrameOrSeries) -> FrameOrSeries:
         --------
         Show which entries in a DataFrame are NA.
 
-        >>> df = pd.DataFrame({'age': [5, 6, np.NaN],
+        >>> df = pd.DataFrame({{'age': [5, 6, np.NaN],
         ...                    'born': [pd.NaT, pd.Timestamp('1939-05-27'),
         ...                             pd.Timestamp('1940-04-25')],
         ...                    'name': ['Alfred', 'Batman', ''],
-        ...                    'toy': [None, 'Batmobile', 'Joker']})
+        ...                    'toy': [None, 'Batmobile', 'Joker']}})
         >>> df
            age       born    name        toy
         0  5.0        NaT  Alfred       None