quick_setup: refactor faulty stage normalization

Normalize and sort the faulty stages in one sweep.

Change-Id: I37b081278318da845b1fe514f2dcb4ee858e1306

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

@@ -465,17 +465,16 @@ def _add_summary_error_message(
     all_stage_errors: list[ValidationErrors] = []
     all_stage_errors.extend(current_errors)
 
-    faulty_stage_indices = [
+    normalized_faulty_stage_indices = sorted(
         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) for index in faulty_stage_indices)
-        if len(faulty_stage_indices) > 1
+        % ", ".join(str(index) for index in normalized_faulty_stage_indices)
+        if len(normalized_faulty_stage_indices) > 1
         else _("Stage %s contains invalid form data. Please correct them and try again.")
-        % faulty_stage_indices[0]
+        % normalized_faulty_stage_indices[0]
     )
 
     all_stage_errors.append(