Wait for the execution to finish when testing procedural macros

This is failing in CI and I cannot see why. What I *can* see is that
the request isn't done yet, so let's add a more explicit
wait. This *shouldn't* matter because I've also tried increasing the
Capybara timeout and that didn't seem to work.

Author: shepmaster

tests/spec/features/automatic_primary_action_spec.rb

@@ -55,6 +55,7 @@
     click_on("Test")
 
     within(:output, :stdout) do
+      expect(page).to_not have_selector(:loader)
       expect(page).to have_content 'a struct with a similar name exists'
     end
   end