chore(deps): update pymdown-extensions requirement from ~=10.8 to ~=10.9

[dependabot[bot]]

Updates the requirements on pymdown-extensions to permit the latest version.

Release notes

Sourced from pymdown-extensions's releases.

10.9

• NEW: Officially support Python 3.13.
• FIX: Snippets: Better handling of cases where URL snippet requests contain no header length.

Commits

• cd7c704 Support Python 3.13 (#2422)
• 72108f0 Bump version
• 368aedc Remove unnecessary logic
• 6b1041f Update JS doc deps
• 973301b Ignore perceived lint issue (#2421)
• ef38568 fix: allow downloading when content-length header is missing (#2413)
• 4ad2baf Update JS doc deps
• 6ed6826 Remove polyfill requirements for Mathjax and do not recommend it in docs
• c8856a3 really drop python<=3.7 support (#2391)
• f1e2fad Update tests to account for latest Ruff and Pygments updates (#2379)
• Additional commits viewable in compare view

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