[SPARK-46586][SQL][TESTS][FOLLOWUP] Replace appended with :+

### What changes were proposed in this pull request?
The pr is following up #44591.

### Why are the changes needed?
Fix issues in comments.
<img width="908" alt="image" src="https://github.com/apache/spark/assets/15246973/deec66a1-1bd1-44bc-9c16-f1fe8bbb14e8">

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
- Pass GA.
- Manually test.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes #44702 from panbingkun/SPARK-46586_fix.

Authored-by: panbingkun <panbingkun@baidu.com>
Signed-off-by: yangjie01 <yangjie01@baidu.com>

sql/core/src/test/scala/org/apache/spark/sql/UDFSuite.scala

@@ -840,7 +840,7 @@ class UDFSuite extends QueryTest with SharedSparkSession {
     Row(ArrayBuffer(100)))
 
      val myUdf2 = udf((a: immutable.ArraySeq[Int]) =>
-      immutable.ArraySeq.unsafeWrapArray[Int](a.appended(5).appended(6).toArray))
+      immutable.ArraySeq.unsafeWrapArray[Int]((a :+ 5 :+ 6).toArray))
     checkAnswer(Seq(Array(1, 2, 3))
       .toDF("col")
       .select(myUdf2(Column("col"))),