deps: update pymdown-extensions requirement from >=10.21.2 to >=10.21.3

Updates the requirements on [pymdown-extensions](https://github.com/facelessuser/pymdown-extensions) to permit the latest version.
- [Release notes](https://github.com/facelessuser/pymdown-extensions/releases)
- [Commits](facelessuser/pymdown-extensions@10.21.2...10.21.3)

---
updated-dependencies:
- dependency-name: pymdown-extensions
  dependency-version: 10.21.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs-requirements.txt

@@ -11,7 +11,7 @@ mkdocs-material>=9.7.6
 mike>=2.2.0
 
 # Markdown extensions (most are included with mkdocs-material, but explicit for clarity)
-pymdown-extensions>=10.21.2
+pymdown-extensions>=10.21.3
 
 # Optional: Useful plugins for enhanced documentation
 # Uncomment if needed: