Summary:
Fix unit test failure in MetricQueryHelperTest
This diff caused it: D41462
Changed error message accordingly

Test Plan: Tested locally using sbt "testOnly com.yugabyte.yw.metrics.MetricQueryHelperTest"

Reviewers: hzare

Reviewed By: hzare

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D41791