lib/test_sort: add a testcase to ensure code coverage

lib/test_sort: add a testcase to ensure code coverage

The addition of an if statement in lib/sort to handle the final unsorted 2
or 3 elements is not covered by existing test cases, leading to incomplete
test coverage.  To ensure comprehensive testing and maintain 100% code
coverage, add a new testcase for scenarios where the if statement is
triggered.

Since the if statement is only triggered when the array length is odd and
the first element is greater than the second element, a testcase is
created using an array length of TEST_LEN - 1 and a suitable random seed
to maintain full code coverage.

Link: https://lkml.kernel.org/r/20240527203011.1644280-5-visitorckw@gmail.com
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Ching-Chun (Jim) Huang <jserv@ccns.ncku.edu.tw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>