Adjust Channels testing matrix.

- Drop testing against Channels 3.
- Test against latest Channels 4.x
- Continue to test against Channels development branch.

Author: carltongibson

README.rst

@@ -20,8 +20,8 @@ There are two available implementations:
 Both layers support a single-server and sharded configurations.
 
 `channels_redis` is tested against Python 3.9 to 3.13, `redis-py` versions 4.6,
-5.0, and the development branch, and Channels versions 3, 4 and the development
-branch there.
+5.0, and the development branch, plus the current Channels version 4.x and the
+development branch there.
 
 Installation
 ------------

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{39,310,311,312,313}-ch{30,40,main}-redis50
+    py{39,310,311,312,313}-ch{4,main}-redis50
     py311-chmain-redis{45,46,50,main}
     qa
 
@@ -10,8 +10,7 @@ extras = tests
 commands =
     pytest -v {posargs}
 deps =
-    ch30: channels>=3.0,<3.1
-    ch40: channels>=4.0,<4.1
+    ch4: channels>=4.0,<5
     chmain: https://github.com/django/channels/archive/main.tar.gz
     redis46: redis>=4.6,<4.7
     redis50: redis>=5.0,<5.1