DataStreamsSnapshotsIT is susceptible to date changes?

[rjernst]

This failure happened in 7.x after an unrelated commit. The failures seem to all be around expecting backing indexes for 5/27, but the tests ran right around midnight and they then got 5/28 backing indexes.

Build scan:
https://gradle-enterprise.elastic.co/s/l5bdqxah6esnc/console-log?task=:x-pack:plugin:data-streams:internalClusterTest

Repro line:

./gradlew ':x-pack:plugin:data-streams:internalClusterTest' --tests "org.elasticsearch.datastreams.DataStreamsSnapshotsIT.testDataStreamNotStoredWhenIndexRequested" -Dtests.seed=39DC7D872D6132FB -Dtests.locale=mt -Dtests.timezone=Pacific/Honolulu -Druntime.java=8

Reproduces locally?:
No

Applicable branches: 7.x, master?

Failure excerpt:

org.elasticsearch.datastreams.DataStreamsSnapshotsIT > testBackingIndexIsNotRenamedWhenRestoringDataStream FAILED

java.lang.AssertionError:
  Expected: is ".ds-ds-2021.05.27-000001"
  but: was ".ds-ds-2021.05.28-000001"
    at __randomizedtesting.SeedInfo.seed([39DC7D872D6132FB:47C0C376B70D2AF6]:0)
    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
    at org.junit.Assert.assertThat(Assert.java:956)
    at org.junit.Assert.assertThat(Assert.java:923)
    at org.elasticsearch.datastreams.DataStreamsSnapshotsIT.testBackingIndexIsNotRenamedWhenRestoringDataStream(DataStreamsSnapshotsIT.java:404)

[elasticmachine]

Pinging @elastic/es-core-features (Team:Core/Features)