requirements.txt: Upgrade Markdown

ERROR: Cannot install Markdown==3.2.1 and mkdocs==1.6.1 because these package versions have conflicting dependencies.

The conflict is caused by:
    The user requested Markdown==3.2.1
    mkdocs 1.6.1 depends on markdown>=3.3.6

Author: adriendupuis

requirements.txt

@@ -1,7 +1,7 @@
 mkdocs==1.6.1
 Pygments==2.15.0
 pymdown-extensions==10.0.1
-Markdown==3.2.1
+Markdown==3.3.6
 mkdocs-material==9.1.1
 mkdocs-macros-plugin==0.7.0
 mkdocs-redirects==1.2.0