Fix postgresql adapter setup for ActionCable tests

(cherry picked from commit e2093c1f678175bde7c37c848686d979427346e1)
(cherry picked from commit d7dbe48273bd9e0adb1de5b52e3cdaeb4a65630b)

actioncable/test/subscription_adapter/postgresql_test.rb

@@ -12,7 +12,7 @@ class PostgresqlAdapterTest < ActionCable::TestCase
     if Dir.exist?(ar_tests)
       require File.join(ar_tests, "config")
       require File.join(ar_tests, "support/config")
-      local_config = ARTest.config["arunit"]
+      local_config = ARTest.config["connections"]["postgresql"]["arunit"]
       database_config.update local_config if local_config
     end