[hotfix] Fix compilation with jdk11

[raminqaf]

What is the purpose of the change

The PR to fix compilation with jdk11

• Nightly broken on Flink master: https://github.com/apache/flink/actions/runs/29887195746

• It runs green on my fork's nightly: https://github.com/raminqaf/flink/actions/runs/29897476389

Brief change log

.toList -> .collect(Collectors.toList())

Verifying this change

run with jdk11

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)

---

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

• Yes (please specify the tool below)

[flinkbot]

CI report:

• 643cdda Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build