[CI] Auditing log fails for API key realm name during BWC with version prior to v7.5

[ywangd]

The failed test UpgradeClusterClientYamlTestSuiteIT.test {p0=mixed_cluster/120_api_key_auth/Test API key authentication will work in a mixed cluster}.

ApiKey realm name is not available in Authentication metadata till v7.5. Hence auditing log fails to retrieve it for older versions.

The failed test has been configured to run only for v7.5 and up. Once this issue is fixed, it can be renabled for older versions by removing these two lines.

Build scan: https://gradle-enterprise.elastic.co/s/zyiwyg5feg74a

[elasticmachine]

Pinging @elastic/es-security (:Security/Audit)

[dakrone]

I believe this is the same issue: https://gradle-enterprise.elastic.co/s/x3e4t32i6m3jq that failed today