Fix Kernel.warn and don't call Warning#warn if a specified category is disabled

Author: andrykonchin

core/warning/warn_spec.rb

@@ -121,7 +121,7 @@ def Warning.warn(msg)
     end
   end
 
-  ruby_bug '#19530', ''...'3.4' do
+  ruby_bug '#20573', ''...'3.4' do
     it "isn't called by Kernel.warn when category is :deprecated but Warning[:deprecated] is false" do
       warn_deprecated = Warning[:deprecated]
       begin