feat(curriculum): Added an additional test for year 2000 (freeCodeCamp#57941)

Author: prabhakaryadav2003

curriculum/challenges/english/25-front-end-development/lab-leap-year-calculator/66c06fad3475cd92421b9ac2.md

@@ -58,6 +58,12 @@ With `2024` as the value of the `year` variable, the `result` should be `2024 is
 assert.strictEqual(isLeapYear(2024), '2024 is a leap year.');
 ```
 
+With `2000` as the value of the `year` variable, the `result` should be `2000 is a leap year.`.
+
+```js
+assert.strictEqual(isLeapYear(2000), '2000 is a leap year.');
+```
+
 With `1900` as the value of the `year` variable, the `result` should be `1900 is not a leap year.`.
 
 ```js