Bump pymdown-extensions from 10.21 to v10.21.2 (#1562)

Co-authored-by: dghubble-renovate[bot] <119624128+dghubble-renovate[bot]@users.noreply.github.com>

Author: dghubble-renovate[bot]

requirements.txt

@@ -1,4 +1,4 @@
 mkdocs==1.6.1
 mkdocs-material==9.7.6
 pygments==2.20.0
-pymdown-extensions==10.21
+pymdown-extensions==10.21.2