fix typo on LeaveOneGroupOut documentation (scikit-learn#29513)

Author: mkdjr

sklearn/model_selection/_split.py

@@ -1279,7 +1279,7 @@ class LeaveOneGroupOut(GroupsConsumerMixin, BaseCrossValidator):
 
     Provides train/test indices to split data such that each training set is
     comprised of all samples except ones belonging to one specific group.
-    Arbitrary domain specific group information is provided an array integers
+    Arbitrary domain specific group information is provided as an array of integers
     that encodes the group of each sample.
 
     For instance the groups could be the year of collection of the samples