Pin cluster CI to redis-py <7.2 to work around initialization bug

redis-py 7.2.0 (released Feb 16) broke async cluster initialization —
their internal NodesManager passes `lib_name` to ClusterNode.__init__
which now raises a deprecation error via the new DriverInfo API (#3880).
We'll unpin once they fix it.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: chrisguidry

.github/workflows/ci.yml

@@ -31,9 +31,11 @@ jobs:
           - name: "Redis 8.0, redis-py >=5"
             redis-version: "8.0"
             redis-py-version: ">=5"
+          # TODO: unpin when redis-py fixes async cluster init with DriverInfo
+          # https://github.com/redis/redis-py/issues/XXXX
           - name: "Redis 8.0 Cluster"
             redis-version: "8.0-cluster"
-            redis-py-version: ">=5"
+            redis-py-version: ">=5,<7.2"
           - name: "Valkey 8.0, redis-py >=5"
             redis-version: "valkey-8.0"
             redis-py-version: ">=5"