Use dmlWithSchema also for on statement in merge-using-query, remove extra line change (#393)

Author: borgiiri

querydsl-libraries/querydsl-sql/src/main/java/com/querydsl/sql/SQLSerializer.java

@@ -597,9 +597,10 @@ public void serializeForMergeUsing(
     handle(usingExpression);
     dmlWithSchema = originalDmlWithSchema;
 
-    append("\n");
     append(templates.getOn());
+    dmlWithSchema = true;
     handle(usingOn);
+    dmlWithSchema = originalDmlWithSchema;
 
     for (final SQLMergeUsingCase when : whens) {
       append("\nwhen ");