Removed 2 unnecessary stubbings in CodePipelineJobPollerTest.java

[ARUS2023]

Issue #, if available:

Description of changes:
In our analysis of the project, we observed that

1. 1 stubbing which stubbed acknowledgeJob method is created but never executed by 8 tests CodePipelineJobPollerTest.testClassLoad, CodePipelineJobPollerTest.shouldThrowWhenJobServiceIsNull, CodePipelineJobPollerTest.shouldThrowWhenJobProcessorIsNull, CodePipelineJobPollerTest.shouldThrowWhenExecutorServiceIsNull, CodePipelineJobPollerTest.shouldPollForJobsWhenThereAreNoActiveWorkerThreads, CodePipelineJobPollerTest.shouldPollForJobsWithBatchSizeWhenNotAllWorkerThreadsAreBusy, CodePipelineJobPollerTest.shouldStartThreadsForAllReturnedJobs, CodePipelineJobPollerTest.shouldNotHandOutWorkToJobProcessorWhenStatusFailed.

2. 1 stubbing which stubbed process method is created but never executed by 10 tests CodePipelineJobPollerTest.testClassLoad, CodePipelineJobPollerTest.shouldThrowWhenJobServiceIsNull, CodePipelineJobPollerTest.shouldThrowWhenJobProcessorIsNull, CodePipelineJobPollerTest.shouldThrowWhenExecutorServiceIsNull, CodePipelineJobPollerTest.shouldPollForJobsWhenThereAreNoActiveWorkerThreads, CodePipelineJobPollerTest.shouldPollForJobsWithBatchSizeWhenNotAllWorkerThreadsAreBusy, CodePipelineJobPollerTest.shouldStartThreadsForAllReturnedJobs, CodePipelineJobPollerTest.shouldNotHandOutWorkToJobProcessorWhenStatusFailed, CodePipelineJobPollerTest.shouldHandleAllRuntimeExceptions, CodePipelineJobPollerTest.shouldReportFailureWhenProcessorReturnsFailure.

Unnecessary stubbings are stubbed method calls that were never realized during test execution. Mockito recommends to remove unnecessary stubbings (https://www.javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/exceptions/misusing/UnnecessaryStubbingException.html).

We propose below a solution to remove the unnecessary stubbings.

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