fix: ignore job-entity run-as value when agent has a job user override

[AWS-Samuel]

What was the problem/requirement? (What/Why)

The worker agent was validating the jobRunAsUser field in the BatchGetJobEntity API response, even when the worker agent was configured with a job user override.

This would lead to issues if a queue was configured with only the opposite system type in the jobRunAsUser. For example, a linux worker with the posix_job_user configuration receives a job, which has a jobRunAsUser value of:

{
    "runAs": "QUEUE_CONFIGURED_USER",
    "windows": {
        "user": "windows-job-user",
        "passwordArn": "<password arn>"
    }
}

Then the worker agent would throw an error here because there is no posix runAs field available, even though it shouldn't matter due to the override.

What was the solution? (How)

Ignore the jobRunAsUser field if the worker agent has a job user override

What is the impact of this change?

The erroneous behavior above no longer occurs.

How was this change tested?

Unit tests added.

Tested on a CMF worker with and without this change.

Confirmed that the worker with this change had a successful job run, while the worker without this change encountered the Expected "jobRunAs" -> "posix" to exist when "jobRunAs" -> "runAs" is "QUEUE_CONFIGURED_USER" but it was not present error

Was this change documented?

No

Is this a breaking change?

No

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[jusiskin]

nit: shouldn't this test belong in test/unit/sessions/job_entities/test_job_details.py instaed, since we're testing behaviour of the JobDetails class?

Marked as a nit because I see this is not precedent as the test above has the same problem. 😞