Summary:
Fix rotate master key UT.
Sometimes the unit test `EncryptionAtRestManagerTest.testRotateMasterKeyWithPreviouslyRotatedKmsConfig` is flaky, probably due to the timestamps being the same and the master key re-encryption test should not be depending solely on the order.

Test Plan:
Manually tested the fix.
Run UTs.
Run itests.

Reviewers: nsingh, sneelakantan, dkumar

Reviewed By: dkumar

Subscribers: yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D40536