Fix: code block syntax

[Mariana-Caetano]

Types of changes

• [ ] New content (guides, endpoints, app documentation)
• [ ] Improvement (make a documentation even better)
• [x] Fix (fix a documentation error)
• [ ] Spelling and grammar accuracy (self-explanatory)

[github-actions[bot]]

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• Couldn't find the corresponding page for docs/faststore/docs/customization/building-sections/list-of-native-sections.mdx. Have you added list-of-native-sections to the navigation.json file? Maybe you can find it in https://developers.vtex.com/docs/guides/faststore/building-sections-list-of-native-sections