tests: ensure jobs persist on server restart

[vkWeb]

Summary

#7951 and #7959 changed server behavior to persist jobs across server restarts. This PR adds tests for this new behavior.

The tests are not at all ideal, I would love to hear ways of making it better!

References

Already referenced.

Reviewer guidance

Do these tests mimic server behavior correctly? Does tests pass?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
• Critical user journeys are covered by Gherkin stories
• Critical and brittle code paths are covered by unit tests

PR process

• PR has the correct target branch and milestone
• PR has 'needs review' or 'work-in-progress' label
• If PR is ready for review, a reviewer has been added. (Don't use 'Assignees')
• If this is an important user-facing change, PR or related issue has a 'changelog' label
• If this includes an internal dependency change, a link to the diff is provided

Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[vkWeb]

cc @rtibbles for review.

[rtibbles]

Should use the real services plugin for the test.

[vkWeb]

@rtibbles sir, I have made updates to these tests. Now we are using real services plugin with scheduler integration.

[rtibbles]

Changes look good, tests are covering important code paths. Thank you!