[FLINK-39405][docs] Fix document escape display errors

[Au-Miner]

What is the purpose of the change

We need to fix the display issue in the document. When '' appears in the document, it is mistakenly escaped as ‘'

Brief change log

• Use ``substitute ''

Verifying this change

cd ./docs
./build_docs.sh
We can find problem in http://localhost:1313/docs/sql/functions/built-in-functions/

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:

• 6f1b3cd Azure: SUCCESS

Bot commands

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

[klion26]

Thanks for the contribution, LGTM

Before

After