Don't allow the `gitlab:env:info` rake task to mutate the list of omniauth providers.

- The test for `rake gitlab:env:info` executed the rake task, which mutated the
  list of omniauth providers, breaking subsequent tests relying on this list.

- I've changed the rake task to duplicate the providers list before modifying it.

lib/tasks/gitlab/info.rake

@@ -53,7 +53,7 @@ namespace :gitlab do
           'Undefined'.color(:red)
         end
 
-      omniauth_providers = Gitlab.config.omniauth.providers
+      omniauth_providers = Gitlab.config.omniauth.providers.dup
       omniauth_providers.map! { |provider| provider['name'] }
 
       puts ""