improve getOwnerDocument

The `instanceof Node` ia not a good idea because `Node` is different
depending on where it runs (main document vs iframe)

packages/@headlessui-react/src/utils/owner.ts

@@ -3,12 +3,11 @@ import { env } from './env'
 
 export function getOwnerDocument<T extends Element | MutableRefObject<Element | null>>(
   element: T | null | undefined
-) {
+): Document | null {
   if (env.isServer) return null
-  if (element instanceof Node) return element.ownerDocument
-  if (element?.hasOwnProperty('current')) {
-    if (element.current instanceof Node) return element.current.ownerDocument
-  }
+  if (!element) return document
+  if ('ownerDocument' in element) return element.ownerDocument
+  if ('current' in element) return element.current?.ownerDocument ?? null
 
-  return document
+  return null
 }