chore(deps): update dependency pymdown-extensions to v10.21.3

Author: renovate[bot]

requirements.txt

@@ -8,5 +8,5 @@ mkdocs-material-extensions==1.3.1
 mkdocs-open-in-new-tab==1.0.8
 mkdocs-redirects==1.2.3
 Pygments==2.19.2
-pymdown-extensions==10.19
+pymdown-extensions==10.21.3
 mkdocs-pages-json-plugin==0.0.2