[DOCS] Fix incorrect PHP array syntax

[FelHell]

Example of getData() return value of a StructuredDataProvider contains incorrect PHP syntax

Summary

This PR can be summarized in the following changelog entry:

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Relevant technical choices:

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Test instructions

This PR can be tested by following these steps:

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Quality assurance

• [ ] I have tested this code to the best of my abilities
• [ ] I have added unittests to verify the code works as intended

Fixes #

[RinyVT]

Thanks for the PR! Checks are failing but that's due to an error in the master branch so I'll merge this.