Fix ES|QL multi_match() signature (elastic#3052) (elastic#3053)

This change was reviewed when it was part of elastic#3048.

(cherry picked from commit cece9a7)

Co-authored-by: Miguel Grinberg <[email protected]>

Author: github-actions[bot]

elasticsearch/esql/functions.py

@@ -649,7 +649,7 @@ def min_over_time(field: ExpressionType) -> InstrumentedExpression:
 
 
 def multi_match(
-    query: ExpressionType, fields: ExpressionType, options: ExpressionType = None
+    query: ExpressionType, *fields: ExpressionType, options: ExpressionType = None
 ) -> InstrumentedExpression:
     """Use `MULTI_MATCH` to perform a multi-match query on the specified field.
     The multi_match query builds on the match query to allow multi-field queries.