Fix "Calendar" Dropdown translation

The translation wasn't being rendered ("Calendar" was being shown instead of "Calendário" in PT-BR).

src/Dropdown.php

@@ -1199,7 +1199,7 @@ public static function getStandardDropdownItemTypes()
                     'KnowbaseItemCategory' => null
                 ],
 
-                _n('Calendar', 'Calendars', 1) => [
+                _n('Calendar', 'Calendars', Session::getPluralNumber()) => [
                     'Calendar' => null,
                     'Holiday' => null
                 ],