Fix rexBuilder issue

Signed-off-by: Tomoyuki Morita <[email protected]>

Author: ykmr1224

core/src/main/java/org/opensearch/sql/calcite/plan/PPLAggregateConvertRule.java

@@ -79,7 +79,7 @@ public void apply(RelOptRuleCall call, LogicalAggregate aggregate, LogicalProjec
     final RelBuilder rawRelBuilder = call.builder();
     final RelBuilderWrapper relBuilder = new RelBuilderWrapper(rawRelBuilder);
     final ExtendedRexBuilder rexBuilder =
-        (ExtendedRexBuilder) aggregate.getCluster().getRexBuilder();
+        new ExtendedRexBuilder(aggregate.getCluster().getRexBuilder());
     final RelFieldBuilder fieldBuilder = new RelFieldBuilder(rawRelBuilder, rexBuilder);
     relBuilder.push(project.getInput());