[hotfix][test] Use unique sink name in CascadedDeltaJoinITCase

[snuyanzin]

What is the purpose of the change

If tests are running in parallel they might reuse the same sink by name and sink will contain unexpected results
The idea is to use more unique sinks

examples of failure
https://github.com/apache/flink/actions/runs/24881538481/job/72892870040#step:12:10351
https://github.com/apache/flink/actions/runs/24895816554/job/72901841273#step:12:10351
https://github.com/apache/flink/actions/runs/24892915051/job/72897348906#step:12:10353
https://github.com/apache/flink/actions/runs/24904840364/job/72933022675#step:12:10352

Brief change log

it is test

Verifying this change

here it is a link to GHA run on my fork https://github.com/snuyanzin/flink/actions/runs/24924498645

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 )

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

[snuyanzin]

@xuyangzhong, @lincoln-lil since were are involved in #27828
it looks like it is a side effect in tests,
for some reason it is almost 100% reproducible in GHA and much rare in Azure

[flinkbot]

CI report:

• 2eea97a Azure: SUCCESS

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[snuyanzin]

here it is a link to GHA run on my fork https://github.com/snuyanzin/flink/actions/runs/24924498645