[FLINK-37404, FLINK-36334][API / Core] Reenable Migration Tests for Filnk 2.x

[SteveStevenpoor]

What is the purpose of the change

This pull request enables migration tests to check snapshot compatibility between Flink 2.x and current versions.

Verifying this change

This change is a trivial rework 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:

• da1a0f3 Azure: FAILURE

Bot commands

The @flinkbot bot supports the following commands:

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

[SteveStevenpoor]

@snuyanzin could you check this please?

There is also 1 disabled test TraversableSerializerUpgradeTest, which can't be enabled right now. There is ClassCastException in traversible-seriallizer-mutable-list test. The previously generated seriallizer-snapshot contains MutableList. Here we try to cast it to ListBuffer:

    override def testDataCondition: Condition[mutable.ListBuffer[Int]] =
      new Condition[mutable.ListBuffer[Int]](
        (l: mutable.ListBuffer[Int]) => Objects.equals(l, mutable.ListBuffer(1, 2, 3)),
        "")

I will file a separate ticket, fix this issue, and enable the remaining test.

I also want to file another ticket to generate snapshots for version 2.3 and update the most recently published version accordingly.