fix(learn): Added another test to check for invalid characters (#41144)

curriculum/challenges/english/02-javascript-algorithms-and-data-structures/regular-expressions/restrict-possible-usernames.md

@@ -98,6 +98,12 @@ Your regex should match `AB1`
 assert(userCheck.test('AB1'));
 ```
 
+Your regex should not match `J%4`
+
+```js
+assert(!userCheck.test('J%4'))
+```
+
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