[Image Resizer] Added AutomationProperties.HelpText to dimensions combo-box (#37122)

Co-authored-by: Stefan Markovic <stefan@janeasystems.com>

src/modules/imageresizer/ui/Properties/Settings.cs

@@ -254,6 +254,7 @@ namespace ImageResizer.Properties
             {
                 _selectedSizeIndex = value;
                 NotifyPropertyChanged();
+                NotifyPropertyChanged(nameof(SelectedSize));
             }
         }