[FLINK-33156][Test]Remove flakiness from tests in OperatorStateBackendTest.java

[asha-boyapati]

What is the purpose of the change

This PR is similar to the following PR which was accepted: #23298

This PR makes the following tests stable:

org.apache.flink.runtime.state.OperatorStateBackendTest#testSnapshotRestoreSync
org.apache.flink.runtime.state.OperatorStateBackendTest#testSnapshotRestoreAsync

The tests are currently flaky because the order of elements returned by iterators is non-deterministic.

This PR fixes the flaky tests by making them independent of the order of elements returned by the iterators.

We detected this using the NonDex tool using the following commands:

mvn edu.illinois:nondex-maven-plugin:2.1.1:nondex -pl flink-runtime -DnondexRuns=10 -Dtest=org.apache.flink.runtime.state.OperatorStateBackendTest#testSnapshotRestoreSync

mvn edu.illinois:nondex-maven-plugin:2.1.1:nondex -pl flink-runtime -DnondexRuns=10 -Dtest=org.apache.flink.runtime.state.OperatorStateBackendTest#testSnapshotRestoreAsync

Please see the following Continuous Integration log that shows the flakiness:
https://github.com/asha-boyapati/flink/actions/runs/6193757385

Please see the following Continuous Integration log that shows that the flakiness is fixed by this change:
https://github.com/asha-boyapati/flink/actions/runs/6194044449

The Jira ticket associated with this PR is as follows:
https://issues.apache.org/jira/browse/FLINK-33156

Brief change log

This PR fixes the flaky tests by making them independent of the order of elements returned by the iterators.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

This change only modifies tests slightly and does not change any underlying code.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[flinkbot]

CI report:

• c159b5a Azure: SUCCESS

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[masteryhx]

Thanks for the pr. Please correct the title firstly: [FLINK-xxx][test] xxx

Could you use NonDex and manul verification to check all these problems together ?
I have seen so many cases, e.g. OperatorStateBackendTest#testRegisterStates, StateBackendMigrationTestBase#testKeyedListStateUpgrade

I think we should handle all these problems in this pr.

[asha-boyapati]

Thanks for your comments. I updated the title. I will look into your suggestion of finding and fixing similar problems together.