[TEST] Different behaviors of SparkContext Conf when building SparkSession

## What changes were proposed in this pull request?
If the created ACTIVE sparkContext is not EXPLICITLY passed through the Builder's API `sparkContext()`, the conf of this sparkContext will also contain the conf set through the API `config()`; otherwise, the conf of this sparkContext will NOT contain the conf set through the API `config()`

## How was this patch tested?
N/A

Author: gatorsmile <gatorsmile@gmail.com>

Closes #18517 from gatorsmile/fixTestCase2.