UI: No Default Icon for Small Python Confirmations

With #118346 we want the new small confirmations to have no icon by
default. I forgot to set this as the default when called via Python.

Pull Request: https://projects.blender.org/blender/blender/pulls/119489

source/blender/makesrna/intern/rna_wm_api.cc

@@ -952,6 +952,7 @@ void RNA_api_wm(StructRNA *srna)
 
   parm = RNA_def_property(func, "icon", PROP_ENUM, PROP_NONE);
   RNA_def_property_enum_items(parm, rna_operator_popup_icon_items);
+  RNA_def_property_enum_default(parm, ALERT_ICON_NONE);
   RNA_def_property_ui_text(parm, "Icon", "Optional icon displayed in the dialog");
 
   api_ui_item_common_translation(func);