Exclude elasticsearch / opensearch shutdown log from find errors

Our builds fail regularly during the functional tests steps due to the log below:

18:16:29  2023-01-26T17:00:22,041 ERROR [opensearch[nuxeoNode][generic][T#1]] [io.netty.util.concurrent.DefaultPromise.rejectedExecution] Failed to submit a listener notification task. Event loop shut down?

This log is present in the server.log file, and it is expected as we're shutting down the server and the embedded elasticsearch / opensearch node.