Fix export service validation for multiple TA modules

[zehata]

Context

As reported by Michael: https://t.me/NUSMods/13410

Implementation

In my previous fix #4277 , I confused ordered with items and the array validation logic fails when the number of TA modules is more than 1.

Other Information

[vercel]

@zehata is attempting to deploy a commit to the modsbot's projects Team on Vercel.

A member of the Team first needs to authorize it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.77%. Comparing base (988c6fd) to head (91db98e).
⚠️ Report is 162 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4284      +/-   ##
==========================================
+ Coverage   54.52%   56.77%   +2.24%     
==========================================
  Files         274      297      +23     
  Lines        6076     6924     +848     
  Branches     1455     1671     +216     
==========================================
+ Hits         3313     3931     +618     
- Misses       2763     2993     +230     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[zehata]

This is similar to the issue that was fixed by 0eef0ba

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Review	Updated (UTC)
nusmods-export	Ready	Preview, Comment	Jan 3, 2026 4:54am
nusmods-website	Ready	Preview, Comment	Jan 3, 2026 4:54am

[leslieyip02]

LGTM!