Set REQUIRE_COURSE_EMAIL_AUTH to True

In production this value is True.

Changing this config file means that developers, by default, will see course email in their local dev and sandbox environments. This is important for full testing of released features. We shouldn't hide a feature we use on prod behind a feature flag locally.
These tests are for the legacy dash feature, which I aim to remove anyway - we don't support legacy. The tests in test_email.py are more comprehensive and test the feature on the instructor dash fully. There are also Lettuce integration tests on the instructor dash.