FIX Only show DatetimeField format description for non-HTML5 inputs

When using HTML5 datetime-local inputs (the default), the scaffolded
description shows an ISO 8601 format example that doesn't match
what browsers actually display in their native date/time pickers.

Fixes #11867

Author: purplespider

src/ORM/FieldType/DBDatetime.php

@@ -182,16 +182,18 @@ public function scaffoldFormField($title = null, $params = null)
         $dateTimeFormat = $field->getDatetimeFormat();
         $locale = $field->getLocale();
 
-        // Set date formatting hints and example
-        $date = static::now()->Format($dateTimeFormat, $locale);
-        $field
-            ->setDescription(_t(
+        // Set date formatting hints and example when not using HTML5 inputs,
+        // as browsers handle format display natively for HTML5 datetime-local fields
+        $field->setAttribute('placeholder', $dateTimeFormat);
+        if (!$field->getHTML5()) {
+            $date = static::now()->Format($dateTimeFormat, $locale);
+            $field->setDescription(_t(
                 'SilverStripe\\Forms\\FormField.EXAMPLE',
                 'e.g. {format}',
                 'Example format',
                 ['format' => $date]
-            ))
-            ->setAttribute('placeholder', $dateTimeFormat);
+            ));
+        }
 
         return $field;
     }