Fix test 3 assertion in 1-write-callbacks.js exercise

[dannyelcf]

Description

One of our students found this bug in our exercises. Follow here the discussion: https://hyfbe.slack.com/archives/C066S1ZP5PH/p1711020395859709

So, this PR fix the Test 3 assertion of the isPalindrome exercise.

-+(*)+- is not a palindrome

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[dannyelcf]

Hello @danielhalasz, hello @samirm00

Could you review this PR, please.

[danielhalasz]

LGTM