[FLINK-27970][tests][JUnit5 migration] flink-hadoop-bulk

[RyanSkraba]

What is the purpose of the change

Update the flink-formats/flink-hadoop-bulk module to AssertJ and JUnit 5 following the JUnit 5 Migration Guide

Brief change log

• Removed dependences on JUnit 4, JUnit 5 Assertions and Hamcrest where possible.

Verifying this change

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

I've verified that there are 31 tests run in this module before and after the refactoring.

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

[flinkbot]

CI report:

• 19cb84ec27f4e14a975d82c1e907343cbb868c70 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[RyanSkraba]

@flinkbot run azure

[RyanSkraba]

Hello! I've rebased this PR to master and fixed the merge conflicts in the meantime.

I will be mostly away from my computer for a couple of weeks, but I'll check in if anything changes!

[snuyanzin]

In general it looks good to me thanks for working on it @RyanSkraba :+1:

I left some minor comments