Update dependency pymdown-extensions to v10.9

[slack-oss-bot]

This PR contains the following updates:

Package	Update	Change
pymdown-extensions	minor	==10.8.1 -> ==10.9

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Release Notes

facelessuser/pymdown-extensions

### [`v10.9`](https://togithub.com/facelessuser/pymdown-extensions/releases/tag/10.9) [Compare Source](https://togithub.com/facelessuser/pymdown-extensions/compare/10.8.1...10.9) #### 10.9 - **NEW**: Officially support Python 3.13. - **FIX**: Snippets: Better handling of cases where URL snippet requests contain no header length.

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