Ban css-backgrounds-4 from autolinking

--HG--
extra : rebase_source : aafa2a2757cc70835f5027272e9a3917263595d3

Author: fantasai

autolinker-config.md

@@ -133,6 +133,7 @@ List in this section specs which should be removed from lists when there's a con
 they'll only be linked to when you specify it explicitly,
 or they're the sole definition of the term.
 
+* css-backgrounds-4
 * css-box-3
 * css-text-4
 * css-inline-3