Enable notifications_redesign feature for beta tests

The new features will be enabled for beta users in tests.

Co-authored-by: David Kang <dkang@suse.com>
Co-authored-by: Eduardo Navarro <enavarro@suse.com>

src/api/spec/support/beta.rb

@@ -1,5 +1,6 @@
 RSpec.configure do |config|
   config.before(:example, beta: true) do
     Flipper.enable(:responsive_ux)
+    Flipper.enable(:notifications_redesign)
   end
 end