[FLINK-38695][table-runtime] Fix wrong metric about left cache request count in DeltaJoinCache

[xuyangzhong]

What is the purpose of the change

Fix wrong metric about left cache request count in DeltaJoinCache.

Brief change log

• Fix wrong metric about left cache request count

Verifying this change

This bug only affects the metric and doesn't affect the computing logic. Existing tests can verify this pr.

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:

• c4cc379 Azure: SUCCESS

Bot commands

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

[xuyangzhong]

I have added the tests, could you please take a look again? @davidradl @rionmonster
The failed case is not related to this fix.