ChannelsLiveServerTestCase causes mail.outbox to always be empty

If I take a test that asserts against the contents of `django.core.mail.outbox`, it will pass with `LiveServerTestCase` but fail with `ChannelsLiveServerTestCase`

Setting `EMAIL_BACKEND = "django.core.mail.backends.locmem.EmailBackend"` explicitly in my settings did not help.

Start with the test that asserts against django.core.mail.outbox and reproduce the difference between LiveServerTestCase and ChannelsLiveServerTestCase. Then inspect how EMAIL_BACKEND and the locmem EmailBackend are configured during the Channels test. Done means the Channels test exposes the expected mail.outbox contents instead of leaving it empty.

Written by the indexing model from the issue text.