FIX: correct readonly timeout

So it only applies in readonly mode

lib/distributed_mutex.rb

@@ -22,10 +22,12 @@ class DistributedMutex
 
     while !try_to_get_lock
       sleep 0.001
-      attempts += 1
       # in readonly we will never be able to get a lock
-      if @using_global_redis && attempts > CHECK_READONLY_ATTEMPT
-        raise Discourse::ReadOnly
+      if @using_global_redis && Discourse.recently_readonly?
+        attempts += 1
+        if attempts > CHECK_READONLY_ATTEMPT
+          raise Discourse::ReadOnly
+        end
       end
     end