Makes tests run slightly faster.

see:
https://jtway.co/speed-up-your-rails-test-suite-by-6-in-1-line-13fedb869ec4

config/environments/test.rb

@@ -41,4 +41,7 @@ Discourse::Application.configure do
   config.assets.digest = false
 
   config.eager_load = false
+
+  config.logger = Logger.new(nil)
+  config.log_level = :fatal
 end