chore(client): typescript migrate _mocks_/challenge-nodes.js (#44439)

Co-authored-by: Shaun Hamilton <shauhami020@gmail.com>

client/src/__mocks__/challenge-nodes.ts

@@ -1,4 +1,19 @@
-const mockChallengeNodes = [
+interface MockChallengeNodes {
+  challenge: {
+    fields: {
+      slug: string;
+      blockName: string;
+    };
+    id: string;
+    block: string;
+    title: string;
+    isPrivate: boolean;
+    superBlock: string;
+    dashedName: string;
+  };
+}
+
+const mockChallengeNodes: MockChallengeNodes[] = [
   {
     challenge: {
       fields: {