fix(curriculum): improve lang type in file-handler script (freeCodeCamp#64789)

Author: pdtrang

curriculum/src/file-handler.ts

@@ -6,7 +6,10 @@ import { fileURLToPath } from 'node:url';
 import debug from 'debug';
 
 import type { Chapter } from '../../shared-dist/config/chapters.js';
-import type { SuperBlocks } from '../../shared-dist/config/curriculum.js';
+import type {
+  SuperBlocks,
+  ChallengeLang
+} from '../../shared-dist/config/curriculum.js';
 import type { Certification } from '../../shared-dist/config/certification-settings.js';
 
 const log = debug('fcc:file-handler');
@@ -153,7 +156,7 @@ export type Challenge = {
   missing?: boolean;
   challengeFiles?: ChallengeFile[];
   solutions?: ChallengeFile[][];
-  lang?: string;
+  lang?: ChallengeLang;
 };
 
 export interface BlockStructure {