fix(client,curriculum): add lang property to Challenge type (#64552)

client/gatsby-node.js

@@ -326,6 +326,7 @@ exports.createSchemaCustomization = ({ actions }) => {
       instructions: String
       isLastChallengeInBlock: Boolean
       isPrivate: Boolean
+      lang: String
       module: String
       msTrophyId: String
       nodules: [Nodule]

curriculum/src/file-handler.ts

@@ -153,6 +153,7 @@ export type Challenge = {
   missing?: boolean;
   challengeFiles?: ChallengeFile[];
   solutions?: ChallengeFile[][];
+  lang?: string;
 };
 
 export interface BlockStructure {