don't pollute test suite with warning message from readonly Redis

lib/discourse_redis.rb

@@ -146,7 +146,7 @@ class DiscourseRedis
     yield
   rescue Redis::CommandError => ex
     if ex.message =~ /READONLY/
-      unless Discourse.recently_readonly?
+      unless Discourse.recently_readonly? || Rails.env.test?
         STDERR.puts "WARN: Redis is in a readonly state. Performed a noop"
       end