Support Redis v4 explicitly

The previous version spelling didn't appear to admit this, however
it actually did. Clarify that both 3.x and 4.x are supported and
test on both. Shouldn't need to lint or typecheck on both however.

Author: PeterJCLaw

poetry.lock

@@ -19,7 +19,7 @@ django = ">=3.2"
 daemonize = "~=2.5.0"
 prometheus-client = "~=0.7"
 typing-extensions = "^4"
-redis = {version = "~=3.*", optional = true}
+redis = {version = ">=3.0,<5", optional = true}
 tqdm = {version = "^4.54.1", optional = true}
 
 [tool.poetry.extras]