[FLINK-26245][runtime-web] fix: render dagre properly after clicking showPlan

[yangjunhan]

What is the purpose of the change

https://issues.apache.org/jira/browse/FLINK-26245

Brief change log

Add missing detectChanges after setting planVisible to true

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): 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:

• 73e68ac Azure: FAILURE

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[github-actions]

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[github-actions]

This PR has been closed since it has not had any activity in 120 days.
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please feel free to re-open the PR and ask for a review.