Stop leaking variables into global namespace.

Set WARN_CREATE_GLOBAL to prevent recurrence.

Fixes zsh-users/zsh-syntax-highlighting#192.

highlighters/main/main-highlighter.zsh

@@ -261,6 +261,7 @@ _zsh_highlight_main_highlighter_highlight_string()
 {
   setopt localoptions noksharrays
   local i j k style varflag
+  local AA
   # Starting quote is at 1, so start parsing at offset 2 in the string.
   for (( i = 2 ; i < end_pos - start_pos ; i += 1 )) ; do
     (( j = i + start_pos - 1 ))