[TEST] Fix Flaky BackupTest#testRestoreDistribution()

[garyparrot]

https://github.com/skiptests/astraea/actions/runs/5096990066/jobs/9163220491#step:5:381

BackupTest > testRestoreDistribution() FAILED
    org.opentest4j.AssertionFailedError: expected: <[...]> but was: <[...]>
        at app//org.junit.jupiter.api.AssertionFailureBuilder.build(AssertionFailureBuilder.java:151)
        at app//org.junit.jupiter.api.AssertionFailureBuilder.buildAndThrow(AssertionFailureBuilder.java:132)
        at app//org.junit.jupiter.api.AssertEquals.failNotEqual(AssertEquals.java:197)
        at app//org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:182)
        at app//org.junit.jupiter.api.AssertEquals.assertEquals(AssertEquals.java:177)
        at app//org.junit.jupiter.api.Assertions.assertEquals(Assertions.java:1142)
        at app//org.astraea.app.backup.BackupTest.testRestoreDistribution(BackupTest.java:70)