FIX: Show the SMTP authentication error for group UI (#27914)

Originally in 964da218173db007fefe6357e96292f5545c513e
we hid the SMTPAuthenticationError message except in
very specific cases. However this message often contains
helpful information from the mail provider, for example
here is a response from Office365:

> 535 5.7.139 Authentication unsuccessful, user is locked by your
organization's security defaults policy. Contact your administrator.

So, we will show the error message in the modal UI instead
of supressing it with a generic message to be more helpful.

spec/requests/groups_controller_spec.rb

@@ -2799,7 +2799,7 @@ RSpec.describe GroupsController do
           post "/groups/#{group.id}/test_email_settings.json", params: params
           expect(response.status).to eq(422)
           expect(response.parsed_body["errors"]).to include(
-            I18n.t("email_settings.smtp_authentication_error"),
+            I18n.t("email_settings.smtp_authentication_error", message: "Invalid credentials"),
           )
         end
       end