Refactor dotenv stuff to internal/util with tests
This was prep work for maybe taking a look at T284227
How to register an account on GitLab. To prevent spam, new accounts are locked until approved by an admin or the approver bot. You can also file an unlock request to expedite access.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
This was prep work for maybe taking a look at T284227