TEST - Use the prodv4 API backend for epidata v4 project testing

[korlaxxalrok]

Prerequisites:

• [ ] Unless it is a hotfix it should be merged against the dev branch
• [ ] Branch is up-to-date with the branch to be merged with, i.e. dev
• [ ] Build is successful
• [ ] Code is cleaned up and formatted

Summary

Use the prodv4 API URL for testing. This is just a PR to generate a preview that we will eventually discard.

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