Fix API integration test for the related endpoint

[obulat]

Fixes

Fixes the failure of related endpoint integration tests when the related items are selected by creator (when the title or tags query do not return any results). For an example see this test run on main (attempt 1): https://github.com/WordPress/openverse/actions/runs/6806564887/attempts/1

Description

This PR adds a check to see if the result is by the same creator (in addition to the checks that there are common words between the related result and the main item)

Marking this as "high" priority because without it, the API tests might be flaky.

Testing Instructions

The CI should pass and the changes should make sense.

Checklist

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• I added or updated tests for the changes I made (if applicable).
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• I ran the DAG documentation generator (if applicable).

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