[FLINK-29495][Connector/Pulsar] Refactor Pulsar tests to disable them on Java 11

[MartijnVisser]

What is the purpose of the change

• There are known issues with Pulsar on Java 11, which is why we want to disable test runs on Java 11. However, the tests still use the JUnit4 annotation for disabling a test on Java 11, which doesn't work. This PR changes that annotation to the JUnit5 equivalent.

Brief change log

• Change @Category to @Tag

Verifying this change

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

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:

• c7a8408 Azure: FAILURE

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