[SPARK-33084][SQL][TESTS][FOLLOW-UP] Fix Scala 2.13 UT failure

### What changes were proposed in this pull request?
Fix UT according to  #29966 (comment)

Change StructType construct from
```
def inputSchema: StructType = StructType(StructField("inputColumn", LongType) :: Nil)
```
to
```
  def inputSchema: StructType = new StructType().add("inputColumn", LongType)
```
The whole udf class is :

```
package org.apache.spark.examples.sql

import org.apache.spark.sql.expressions.{MutableAggregationBuffer, UserDefinedAggregateFunction}
import org.apache.spark.sql.types._
import org.apache.spark.sql.Row

class Spark33084 extends UserDefinedAggregateFunction {
  // Data types of input arguments of this aggregate function
  def inputSchema: StructType = new StructType().add("inputColumn", LongType)

  // Data types of values in the aggregation buffer
  def bufferSchema: StructType =
    new StructType().add("sum", LongType).add("count", LongType)
  // The data type of the returned value
  def dataType: DataType = DoubleType
  // Whether this function always returns the same output on the identical input
  def deterministic: Boolean = true
  // Initializes the given aggregation buffer. The buffer itself is a `Row` that in addition to
  // standard methods like retrieving a value at an index (e.g., get(), getBoolean()), provides
  // the opportunity to update its values. Note that arrays and maps inside the buffer are still
  // immutable.
  def initialize(buffer: MutableAggregationBuffer): Unit = {
    buffer(0) = 0L
    buffer(1) = 0L
  }
  // Updates the given aggregation buffer `buffer` with new input data from `input`
  def update(buffer: MutableAggregationBuffer, input: Row): Unit = {
    if (!input.isNullAt(0)) {
      buffer(0) = buffer.getLong(0) + input.getLong(0)
      buffer(1) = buffer.getLong(1) + 1
    }
  }
  // Merges two aggregation buffers and stores the updated buffer values back to `buffer1`
  def merge(buffer1: MutableAggregationBuffer, buffer2: Row): Unit = {
    buffer1(0) = buffer1.getLong(0) + buffer2.getLong(0)
    buffer1(1) = buffer1.getLong(1) + buffer2.getLong(1)
  }
  // Calculates the final result
  def evaluate(buffer: Row): Double = buffer.getLong(0).toDouble / buffer.getLong(1)
}
```

### Why are the changes needed?
Fix UT for scala 2.13

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

### How was this patch tested?
Existed UT

Closes #30980 from AngersZhuuuu/spark-33084-followup.

Authored-by: angerszhu <angers.zhu@gmail.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

Author: AngersZhuuuu