Unlock channels_redis and implement the workaround from the issue to use pub/sub instead

Pipfile

@@ -46,6 +46,7 @@ tika = "*"
 # TODO: This will sadly also install daphne+dependencies,
 #  which an ASGI server we don't need. Adds about 15MB image size.
 channels = "~=3.0"
+channels-redis = "*"
 uvicorn = {extras = ["standard"], version = "*"}
 concurrent-log-handler = "*"
 "pdfminer.six" = "*"
@@ -62,9 +63,6 @@ bleach = "*"
 #
 # Pin this until piwheels is building 1.9 (see https://www.piwheels.org/project/scipy/)
 scipy = "==1.8.1"
-# Locked version until https://github.com/django/channels_redis/issues/332
-# is resolved
-channels-redis = "==3.4.1"
 
 [dev-packages]
 coveralls = "*"