[fix] Broken CI: Bump Pelican to latest version

This updates jinja, and markupsafe, to avoid following error:
ImportError: cannot import name 'soft_unicode' from 'markupsafe'

requirements.txt

-pelican==4.5.4
+pelican==4.7.2
 Markdown==3.3.4
 beautifulsoup4==4.9.3