ref: upgrade cssutils to avoid DeprecationWarning for logger.warn (#34244)

requirements-base.txt

@@ -91,7 +91,7 @@ hiredis==0.3.1
 cffi==1.14.5
 
 # not directly used, but pinned for toronado because it doesn't pin these
-cssutils==1.0.2
+cssutils==2.4.0
 cssselect==1.0.3
 
 # sentry-plugins specific dependencies