[SPARK-31372][SQL][TEST][FOLLOW-UP] Improve ExpressionsSchemaSuite so that easy to track the diff.

[beliefer]

What changes were proposed in this pull request?

This PR follows up #28194.
As discussed at https://github.com/apache/spark/pull/28194/files#r418418796.
This PR will improve ExpressionsSchemaSuite so that easy to track the diff.
Although ExpressionsSchemaSuite at line

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

Line 165 in b7cde42

assert(lines.size == outputs.size +8,

just want to compare the total size between expected output size and the newest output size, the scalatest framework will output the extra information contains all the content of expected output and newest output.
This PR will try to avoid this issue.
After this PR, the exception looks like below:

[info] - Check schemas for expression examples *** FAILED *** (7 seconds, 336 milliseconds)
[info] 340 did not equal 341 Expected 332 blocks in result file but got 333. Try regenerate the result files. (ExpressionsSchemaSuite.scala:167)
[info] org.scalatest.exceptions.TestFailedException:
[info] at org.scalatest.Assertions.newAssertionFailedException(Assertions.scala:530)
[info] at org.scalatest.Assertions.newAssertionFailedException$(Assertions.scala:529)
[info] at org.scalatest.FunSuite.newAssertionFailedException(FunSuite.scala:1560)
[info] at org.scalatest.Assertions$AssertionsHelper.macroAssert(Assertions.scala:503)
[info] at org.apache.spark.sql.ExpressionsSchemaSuite.$anonfun$new$1(ExpressionsSchemaSuite.scala:167)

Why are the changes needed?

Make the exception more concise and clear.

Does this PR introduce any user-facing change?

'No'.

How was this patch tested?

Jenkins test.

[beliefer]

cc @HyukjinKwon@cloud-fan

[SparkQA]

Test build #122171 has finished for PR 28430 at commit d4e50d6.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #122173 has finished for PR 28430 at commit bf7f621.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #122240 has finished for PR 28430 at commit 951bf24.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[beliefer]

retest this please

[SparkQA]

Test build #122257 has finished for PR 28430 at commit 951bf24.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

retest this please

[SparkQA]

Test build #122261 has finished for PR 28430 at commit 951bf24.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

Merged to master and branc-3.0.

[beliefer]

@HyukjinKwon Thanks for your help!