When converting to epub in Calibre make sure ‘Preserve cover aspect ratio’ is checked in Epub output. That produces:
<?xml version='1.0' encoding='utf-8'?>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<meta name="calibre:cover" content="true"/>
<title>Cover</title>
<style type="text/css" title="override_css">
@page {padding: 0pt; margin:0pt}
body { text-align: center; padding:0pt; margin: 0pt; }
</style>
</head>
<body>
<div>
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" width="100%" height="100%" viewBox="0 0 469 751" preserveAspectRatio="xMidYMid meet">
<image width="469" height="751" xlink:href="cover.jpeg"/>
</svg>
</div>
</body>
</html>
Strictly speaking the value ‘none’ is allowed for the preserveAspectRatio in epub files but epubcheck will reject it unless it’s followed by a space. Checking the ‘Preserve cover aspect ratio’ will fix this.