ApplicationSetting.current doesn't work well in tests

Therefore we prefer
`Gitlab::CurrentSettings.current_application_settings`
and fix the tests by setting default_artifacts_expire_in to 0
to restore the original behaviour.

app/models/ci/build.rb

@@ -518,7 +518,8 @@ module Ci
         if expire_in
           expire_in
         else
-          ApplicationSetting.current.default_artifacts_expire_in
+          Gitlab::CurrentSettings.current_application_settings
+            .default_artifacts_expire_in
         end
 
       self.artifacts_expire_in = value

spec/requests/ci/api/builds_spec.rb

@@ -638,6 +638,8 @@ describe Ci::API::Builds do
             end
 
             before do
+              stub_application_setting(default_artifacts_expiration: 0)
+
               post(post_url, post_data, headers_with_token)
             end