[FLINK-27315] Fix the demo of MemoryStateBackendMigration

[EchoLee5]

What is the purpose of the change

JobManagerStateBackend changed to JobManagerCheckpointStorage

Brief change log

JobManagerStateBackend changed to JobManagerCheckpointStorage

Verifying this change

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

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[flinkbot]

CI report:

• 872b761 Azure: CANCELED
• b35d628 Azure: PENDING
• 17c1a7c UNKNOWN

Bot commands

The @flinkbot bot supports the following commands:

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

[Myasuka]

@EchoLee5 I think the patch is good. However, this PR cannot be merged due to current commits in your EchoLee5:master branch. You should let your commit on top of the latest master branch without any commit like Merge branch 'apache:master' into master, in general, we would use different branch instead of the master branch in your forked repo to create the pull request.

[EchoLee5]

@EchoLee5 I think the patch is good. However, this PR cannot be merged due to current commits in your EchoLee5:master branch. You should let your commit on top of the latest master branch without any commit like Merge branch 'apache:master' into master, in general, we would use different branch instead of the master branch in your forked repo to create the pull request.

@Myasuka Thanks for the suggestion, I will change the pr and resubmit

[Myasuka]

It seems you still did not get what I mean, I think you'd better create another PR based on your another forked branch instead of EchoLee5:master branch.

[EchoLee5]

It seems you still did not get what I mean, I think you'd better create another PR based on your another forked branch instead of EchoLee5:master branch.

Sorry, I misunderstood your point, I closed this pr first