fix(curriculum): missing back-tick for telephone-validator (freeCodeCamp#55982)

Author: akhilk2802

curriculum/challenges/english/15-javascript-algorithms-and-data-structures-22/build-a-telephone-number-validator-project/build-a-telephone-number-validator.md

@@ -35,7 +35,7 @@ Note that the area code is required. Also, if the country code is provided, you
 1. When the `#user-input` element contains `1 555-555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 1 555-555-5555"`
 1. When the `#user-input` element contains `1 (555) 555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 1 (555) 555-5555"`
 1. When the `#user-input` element contains `5555555555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 5555555555"`
-1. When the `#user-input` element contains `555-555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 555-555-5555"
+1. When the `#user-input` element contains `555-555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 555-555-5555"`
 1. When the `#user-input` element contains `(555)555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: (555)555-5555"`
 1. When the `#user-input` element contains `1(555)555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Valid US number: 1(555)555-5555"`
 1. When the `#user-input` element contains `555-5555` and the `#check-btn` element is clicked, the `#results-div` element should contain the text `"Invalid US number: 555-5555"`