Error in Yandex cvc-elt.1.a: Cannot find the declaration of element 'urlset'. How to decide?

Question

XML

Hello. Tell me the details of this error, otherwise for so long I first encountered it and I don’t understand what’s wrong.

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
<url>
<loc>
http://sait.ru/alushta/kvartiri/6-k-kvartira-299-m-9-9-et-adv28414.html
</loc>
<changefreq>weekly</changefreq>
<priority>0.9</priority>
</url>
<url>
</urlset>