Update dependency pymdown-extensions to v10.21.2 (#12267)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

site/requirements.txt

@@ -8,4 +8,4 @@ mkdocs-minify-plugin==0.8.0
 mkdocs-monorepo-plugin==1.1.2
 mkdocs-redirects==1.2.3
 mkdocs-rss-plugin==1.17.9
-pymdown-extensions==10.21
+pymdown-extensions==10.21.2