[FLINK-39768][tests][JUnit5 migration] Module: flink-avro - AvroStreamingFileSinkITCase straggler

[spuru9]

What is the purpose of the change

Migrate the last remaining JUnit 4 test in flink-formats/flink-avro (AvroStreamingFileSinkITCase) to JUnit 5 (Jupiter). The rest of the module was migrated under FLINK-26232 (fix 1.15.0); this file was a leftover. This is the sole change required to remove JUnit 4 from the module.

JIRA: FLINK-39768 (sub-task of FLINK-25325)

Brief change log

• org.junit.* imports → org.junit.jupiter.api.*.
• @Rule public Timeout timeoutPerTest = Timeout.seconds(20) → class-level @Timeout(value = 20).
• extends AbstractTestBaseJUnit4 → extends AbstractTestBase (the JUnit 5 sibling).
• TEMPORARY_FOLDER.newFolder() (static @ClassRule field on the JUnit 4 base) → TempDirUtils.newFolder(temporaryFolder.toPath()) (instance @TempDir on the JUnit 5 base).
• Drop public on the test class and test methods per the Flink JUnit 5 Migration Guide.

No production code is touched.

Verifying this change

./mvnw -pl flink-formats/flink-avro test -Dtest=AvroStreamingFileSinkITCase

Result: 3 tests run, 0 failures, 0 errors, 0 skipped, matching the pre-migration baseline.

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 — Claude Code

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CI report:

• 394b3bf Azure: FAILURE

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