Fix documentation typo - function components introduction.mdx

[devfbe]

Description

Just add a missing 'l' to the closing HelloWorld tag in the function components documentation (introduction.mdx)

Checklist

• [x] I have reviewed my own code
• [ ] I have added tests

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit adc1883):

https://yew-rs--pr3417-devfbe-fix-typo-in-f-bilc6kkk.web.app

_{(expires Sun, 01 Oct 2023 20:41:19 GMT)}

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