[ruby/prism] Fix example marker for case statement predicate

ruby/prism@2ddedf650a

Author: rwstauner

prism/config.yml

@@ -1800,7 +1800,7 @@ nodes:
           Represents the predicate of the case statement. This can be either `nil` or any [non-void expressions](https://github.com/ruby/prism/blob/main/docs/parsing_rules.md#non-void-expression).
 
               case true; when false; end
-              ^^^^
+                   ^^^^
       - name: conditions
         type: node[]
         kind: WhenNode