minor variable adjustment

> The function changes from `forEach` to `for...of`, but then returns early from within the loop body. The early return will exit the entire function, not just the loop iteration. This is likely a bug - the original `forEach` would have continued to check other environment variables. If an early exit is intended for the first missing variable, this works correctly, but verify this is the desired behavior.

_Originally posted by @Copilot in [#431](https://github.com/CenterForDigitalHumanities/TPEN-services/pull/431/changes#r2608032650)_