NIFI-15766 - Fix flaky ConnectorCrudIT.testSecretReferences

[pvillard31]

Summary

NIFI-15766 - Fix flaky ConnectorCrudIT.testSecretReferences

In StandardAsynchronousWebRequest.markStepComplete, the complete volatile field was written before results, while the entity creation methods in the Resource classes read results before complete. This allowed a reader to observe complete=true with results=null when the verification task completed between the two non-atomic volatile reads, breaking the happens-before chain.

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