[hotfix][build] Update Python CI Java version to fix CI

[hlteoh37]

Purpose of the change

Specify Java version to 11 to allow CI to run against the latest Flink artefacts.

Verifying this change

This change is already covered by existing tests, such as Github workflow.

Significant changes

(Please check any boxes [x] if the answer is "yes". You can first publish the PR and check them afterwards, for convenience.)

• [ ] Dependencies have been added or upgraded
• [ ] Public API has been changed (Public API is any class annotated with @Public(Evolving))
• [ ] Serializers have been changed
• [ ] New feature has been introduced
  • If yes, how is this documented? (not applicable / docs / JavaDocs / not documented)