MINOR: Improve test assertions for IQv2

[vvcephei]

I saw one isolated test failure for these tests, but I couldn't confirm whether the result was missing a whole partition or whether the iterator for the partition was empty, so I'm adding the actual result to the failure message to tell the difference.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[bbejeck]

LGTM pending test results

[vvcephei]

The test failures were unrelated:

Build / ARM / org.apache.kafka.streams.integration.NamedTopologyIntegrationTest.shouldRemoveOneNamedTopologyWhileAnotherContinuesProcessing
[Build / JDK 11 and Scala 2.13 / kafka.admin.LeaderElectionCommandTest.[1] Type=Raft, Name=testPathToJsonFile, Security=PLAINTEXT](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.admin/LeaderElectionCommandTest/Build___JDK_11_and_Scala_2_13____1__Type_Raft__Name_testPathToJsonFile__Security_PLAINTEXT/)
[Build / JDK 11 and Scala 2.13 / kafka.api.ConsumerBounceTest.testClose()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.api/ConsumerBounceTest/Build___JDK_11_and_Scala_2_13___testClose__/)
[Build / JDK 11 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_11_and_Scala_2_13___testThreadPoolResize__/)
[Build / JDK 11 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_11_and_Scala_2_13___testThreadPoolResize___2/)
Build / JDK 11 and Scala 2.13 / org.apache.kafka.streams.integration.EosIntegrationTest.shouldWriteLatestOffsetsToCheckpointOnShutdown[at_least_once]
Build / JDK 11 and Scala 2.13 / org.apache.kafka.streams.integration.NamedTopologyIntegrationTest.shouldRemoveOneNamedTopologyWhileAnotherContinuesProcessing
[Build / JDK 8 and Scala 2.12 / kafka.api.ConsumerBounceTest.testClose()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.api/ConsumerBounceTest/Build___JDK_8_and_Scala_2_12___testClose__/)
Build / JDK 8 and Scala 2.12 / org.apache.kafka.streams.integration.NamedTopologyIntegrationTest.shouldRemoveOneNamedTopologyWhileAnotherContinuesProcessing
[Build / JDK 17 and Scala 2.13 / kafka.server.DynamicBrokerReconfigurationTest.testThreadPoolResize()](https://ci-builds.apache.org/job/Kafka/job/kafka-pr/job/PR-11828/1/testReport/junit/kafka.server/DynamicBrokerReconfigurationTest/Build___JDK_17_and_Scala_2_13___testThreadPoolResize__/)