[FLINK-30098] Migrate DynamoDb unit tests to JUnit5

[hlteoh37]

What is the purpose of the change

Migrate DynamoDb unit tests to JUnit5

Verifying this change

Ran unit tests locally and verified all passed.

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? n/a

[YuriGusev]

Thanks for fixing. I thought I changed these tests. Probably got lost during rebase/merges.

[dannycranmer]

Thanks @hlteoh37, LGTM