quick_setup: fix off by one error

When there was only one error when submitting the quick setup
configuration, the wrong stage index would be printed (zero based
index).

Let's normalize the stages in one go, making it based on 1.

CMK-21713

Change-Id: I5890c0d825ce3e4f7ba77d012f5c6afffc735c49

Author: logan-connolly

cmk/gui/openapi/endpoints/quick_setup/__init__.py

@@ -466,13 +466,13 @@ def _add_summary_error_message(
     all_stage_errors.extend(current_errors)
 
     faulty_stage_indices = [
-        err.stage_index for err in current_errors if err.stage_index is not None
+        err.stage_index + 1 for err in current_errors if err.stage_index is not None
     ]
     faulty_stage_indices.sort()
 
     msg = (
         _("Stages %s contain invalid form data. Please correct them and try again.")
-        % ", ".join(str(index + 1) for index in faulty_stage_indices)
+        % ", ".join(str(index) for index in faulty_stage_indices)
         if len(faulty_stage_indices) > 1
         else _("Stage %s contains invalid form data. Please correct them and try again.")
         % faulty_stage_indices[0]