fix(curriculum): accept both arrow and regular empty function (freeCodeCamp#57087)

Author: sulaiman-dev

curriculum/challenges/english/15-javascript-algorithms-and-data-structures-22/learn-regular-expressions-by-building-a-spam-filter/641cd91d28bebe226f765d86.md

@@ -26,7 +26,7 @@ assert.match(code, /checkMessageButton\.addEventListener\(\s*('|"|`)click\1\s*,/
 Your `.addEventListener()` method should have an empty callback function.
 
 ```js
-assert.match(code, /checkMessageButton\.addEventListener\(\s*('|"|`)click\1\s*,\s*\(\s*\)\s*=>\s*\{\s*\}\s*\)/);
+assert.match(code, /checkMessageButton\.addEventListener\(\s*('|"|`)click\1\s*,\s*(\(\s*\)\s*=>\s*\{\s*\}|function\s*\(\s*\)\s*\{\s*\})\s*\)/);
 ```
 
 # --seed--