Ensure multivalues are sorted in MvJoinKeyOnTheDataNode (elastic#119505)

The test failed as values in language_name appeared in reverse order:
row 3 column 2:0: expected "[Mv-Lang, Mv-Lang2]" but was "[Mv-Lang2, Mv-Lang]"

Author: idegtiarenko

x-pack/plugin/esql/qa/testFixtures/src/main/resources/lookup-join.csv-spec

@@ -419,6 +419,7 @@ FROM employees
 | EVAL language_code = emp_no % 10
 | LOOKUP JOIN languages_lookup_non_unique_key ON language_code
 | SORT emp_no
+| EVAL language_name = MV_SORT(language_name)
 | KEEP emp_no, language_code, language_name
 ;