add hyphen to gYearMonth with days-from-month

xquery/date.xqm

@@ -49,7 +49,7 @@ declare %private function date:getCastableDate($date as xs:string, $latest as xs
         if($latest) then xs:date(concat($date,'-12-31'))
         else xs:date(concat($date,'-01-01'))
     else if($date castable as xs:gYearMonth) then
-        if($latest) then xs:date(concat($date, functx:days-in-month(xs:date(concat($date,'-01')))))
+        if($latest) then xs:date(concat($date, '-', functx:days-in-month(xs:date(concat($date,'-01')))))
         else xs:date(concat($date,'-01'))
     else()
 };