Fix GroupBy.apply doc examples rendering (#12994)

Closes #12986.

Authors:
  - https://github.com/brandon-b-miller

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

URL: #12994

python/cudf/cudf/core/groupby/groupby.py

@@ -1278,13 +1278,14 @@ def mult(df):
         ``engine='jit'`` may be used to accelerate certain functions,
         initially those that contain reductions and arithmetic operations
         between results of those reductions:
+
         >>> import cudf
         >>> df = cudf.DataFrame({'a':[1,1,2,2,3,3], 'b':[1,2,3,4,5,6]})
         >>> df.groupby('a').apply(
-        ...     lambda group: group['b'].max() - group['b'].min(),
-        ...     engine='jit'
+        ...   lambda group: group['b'].max() - group['b'].min(),
+        ...   engine='jit'
         ... )
-        a  None
+           a  None
         0  1     1
         1  2     1
         2  3     1