fix(challenge): Additional test cases for 'Escape Sequences in Strings'

[billy-reilly]

This is a revised PR for my previous PR #13090 with the changes requested by @Greenheart

Pre-Submission Checklist

• Your pull request targets the staging branch of freeCodeCamp.
• Branch starts with either fix/, feature/, or translate/ (e.g. fix/signin-issue)
• You have only one commit (if not, squash them into one commit).
• All new and existing tests pass the command npm test. Use git commit --amend to amend any fixes.

Type of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)
• Add new translation (feature adding new translations)

Checklist:

• Tested changes locally.
• Closes currently open issue (replace XXXX with an issue no): Closes Need more test for Escape Sequences in Strings. #12410 and Confusing error message. #11792

Description

Additional test cases and hints added to reduce confusion and help users find the correct solution

[Greenheart]

@billy-reilly Thanks for the update!

I'm afraid I wasn't clear enough - you could just have used git commit --amend and git push origin <your-branch> -f to update the previous PR without having to reopen it.

But it's no problem, I'll just review this one ☺️

[Greenheart]

@billy-reilly Thanks for the fix! 😄