[FLINK-30640][SqlClient] Fix unstable ctas test in CliClientITCase

[lsyldliu]

What is the purpose of the change

Fix the unstable ctas test in CliClientITCase, we should wait for the insert query to finish first, then query the table

Verifying this change

This change is already covered by existing tests.

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 documented)

[flinkbot]

CI report:

• ed1665a Azure: SUCCESS

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[fsk119]

LGTM