[FLINK-32848][tests][JUnit5 migration] Migrate flink-runtime/rpc tests to JUnit5

[X-czh]

What is the purpose of the change

Migrate flink-runtime/rpc tests to JUnit5.

Verifying this change

The change itself is for migrating UT.

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:

• c847c26 Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

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

[X-czh]

Hi @1996fanrui, could you review the change when you are free, much appreciated~

[ferenc-csaky]

Thanks for the contribution @X-czh! Left some comments.

[X-czh]

@ferenc-csaky Thanks for the suggestions! I've improved them, help review again when you have time, thanks in advance~

[ferenc-csaky]

Thanks for making the changes @X-czh! LGTM!

[X-czh]

Squashed commits to clean up the commit history. @FangYongs Could you help take a look when you have time?

[X-czh]

@FangYongs Thanks for the careful review, I've corrected the two mistakes, please review again when you have time~

[FangYongs]

Thanks @X-czh for contributions, LGTM

[FangYongs]

The CI is failed due to failed download of node-16.13.2-linux-x64.tar.gz, re-run it

[FangYongs]

@flinkbot run azure