fix flakey test_agent_jobs_integration

[eric-weaver]

What does this PR do?

• Fix flaky test_agent_jobs_integration by making it self-contained instead of implicitly depending on test_history_output having run first
• The test was failing with Cannot insert the value NULL into column 'job_id' because ACTIVITY_INSERTION_QUERY references 'Job 2' via a subquery (SELECT job_id FROM msdb.dbo.sysjobs WHERE name = 'Job 2'), but 'Job 2' was only created inside a separate test (test_history_output). When test ordering, -k filtering, or a prior test failure caused test_agent_jobs_integration to run without test_history_output completing first, the subquery returned NULL and the INSERT failed.

Motivation

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[github-actions]

⚠️ Recommendation: Add qa/skip-qa label

This PR does not modify any files shipped with the agent.

To help streamline the release process, please consider adding the qa/skip-qa label if these changes do not require QA testing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.39%. Comparing base (9bad3d6) to head (5c994cf).
⚠️ Report is 32 commits behind head on master.

Additional details and impacted files

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