fix(curriculum): modify regex backreference example code (freeCodeCamp#59643)

Author: Supravisor

curriculum/challenges/english/25-front-end-development/lecture-working-with-regular-expressions/6733c5f20cc9584cada942a4.md

@@ -91,7 +91,7 @@ This current expression won't ensure that the number of `o` characters is the sa
 Inside a regular expression, a backreference is denoted with a backslash followed by the number of the capture group:
 
 ```js
-const regex = /free(co+de)camp.*free(co+de)camp/i;
+const regex = /free(co+de)camp.*free\1camp/i;
 console.log(regex.test("freecooooodecamp is great i love freecooooodecamp")); // true
 console.log(regex.test("freecooooodecamp is great i love freecodecamp")); // false
 ```