testcontainers: fix left-nav formatting (#22147)

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## Description

Moved topic out of folder to prevent left-nav drop-down with no child
content.

![image](https://github.com/user-attachments/assets/9488a308-8ef3-454c-bcee-906afdc13700)

![image](https://github.com/user-attachments/assets/2e2d4695-36c9-456a-a15d-5d57f47466b7)


## Related issues or tickets

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## Reviews

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- [ ] Editorial review

Signed-off-by: Craig <[email protected]>

Author: craig-osterhout