Download all submissions feature for students failing in production

[jhs-panda]

Your environment Feature in PR #2137 is failing in CMU production.

Error Message: Subject: [CMU-Autolab-Prod Error] users#download_all_submissions (Zip::EntryExistsError) "add failed. Entry autolab_all_submissio... A Zip::EntryExistsError occurred in users#download_all_submissions:

add failed. Entry autolab_all_submissions_2024-08-13/15213-s21/attacklab/attacklab_<XXX>@andrew.cmu.edu_all.txt already exists app/controllers/users_controller.rb:185:in `block (2 levels) in download_all_submissions'

Steps To Reproduce Unable to reproduce in Autolab environment at this point.