Certificate: Set Default Bday Format il_CAL_DATE

See: https://mantis.ilias.de/view.php?id=43240
(cherry picked from commit a4c6eab)

Author: kergomard

components/ILIAS/Certificate/classes/Placeholder/Values/class.ilDefaultPlaceholderValues.php

@@ -54,7 +54,7 @@ public function __construct(
         require_once __DIR__ . '/../../../../Calendar/classes/class.ilDateTime.php'; // Required because of global contant IL_CAL_DATE
 
         $this->dateFormat = $dateFormat ?? IL_CAL_UNIX;
-        $this->birthdayDateFormat = $birthdayDateFormat ?? IL_CAL_UNIX;
+        $this->birthdayDateFormat = $birthdayDateFormat ?? IL_CAL_DATE;
 
         if (null === $language) {
             global $DIC;