📝 Properly indent code snippets for the documentation (#5383)

**Description**

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Our documentation references live coding code sections. These sections
offer users ways to test fast-check from their own browser.

At the moment, the code in these sections was un-properly indented with
an extra 2-space-gap at the beginning of each line of code. This PR just
drops this extra spacing.

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- [x] The name of my PR follows [gitmoji](https://gitmoji.dev/)
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- [x] My PR references one of several related issues (if any)
- [x] New features or breaking changes must come with an associated
Issue or Discussion
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impacts properly
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(when applicable)

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**Advanced**

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- [x] Category: 📝 Add or update documentation
- [x] Impacts: None

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