Update dependency Markdown to v3.5.1

Author: slack-oss-bot

.github/workflows/mkdocs-requirements.txt

@@ -3,7 +3,7 @@ future==0.18.3
 Jinja2==3.1.2
 livereload==2.6.3
 lunr==0.7.0.post1
-Markdown==3.4.4
+Markdown==3.5.1
 MarkupSafe==2.1.3
 mkdocs==1.5.3
 mkdocs-macros-plugin==1.0.4