[BUG] query_insights tests flaky

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What is the bug?

From https://github.com/opensearch-project/opensearch-api-specification/actions/runs/12242182451/job/34148934118?pr=711

FAILED  insights/top_queries.yaml (tests/plugins/query_insights/insights/top_queries.yaml)
    FAILED  CHAPTERS
        PASSED  Retrieve default top queries.
            PASSED  REQUEST BODY
            PASSED  RESPONSE STATUS
            PASSED  RESPONSE PAYLOAD BODY
            PASSED  RESPONSE PAYLOAD SCHEMA
            SKIPPED RESPONSE OUTPUT VALUES
        FAILED  Retrieve top queries by latency.
            PASSED  PARAMETERS
                PASSED  type
            PASSED  REQUEST BODY
            PASSED  RESPONSE STATUS
            PASSED  RESPONSE PAYLOAD BODY
            FAILED  RESPONSE PAYLOAD SCHEMA (data/top_queries/0/source/query/bool/must/0/match/title/zero_terms_query MUST be equal to one of the allowed values: all, none, data/top_queries/0/source/query/bool/must must be object, data/top_queries/0/source/query/bool/must must be object, data/top_que, ...)

How can one reproduce the bug?

Unclear.

What is the expected behavior?

Tests to pass consistently.

What is your host/environment?

CI/CD GHA

Do you have any screenshots?

Do you have any additional context?

Likely a response that varies if you query too slow/fast/out of order.

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@ansjcy if you have any idea what this API intermittently returns that doesn't match the spec (a null?) and can correct it, that would be much appreciated.