AC: skip PG adapter tests if the db isn't available

actioncable/test/subscription_adapter/postgresql_test.rb

@@ -15,8 +15,15 @@ class PostgresqlAdapterTest < ActionCable::TestCase
       local_config = ARTest.config['arunit']
       database_config.update local_config if local_config
     end
+
     ActiveRecord::Base.establish_connection database_config
 
+    begin
+      ActiveRecord::Base.connection
+    rescue
+      skip "Couldn't connect to PostgreSQL: #{database_config.inspect}"
+    end
+
     super
   end