[ST] Fix StrimziUpgradeST.testUpgradeAcrossVersionsWithUnsupportedKafkaVersion test to run only when there is really an unsupported Kafka version across versions

[ST] Fix StrimziUpgradeST.testUpgradeAcrossVersionsWithUnsupportedKafkaVersion test to run only when there is really an unsupported Kafka version across versions #14617