test: Fix XML parser security tests on Xbox (#4695)

Xbox seems to treat SVG and/or XML a little differently than other
platforms, which led to a test failure on that platform. That went
unnoticed because Xbox is offline in our lab. The issue was discovered
while working to restore that platform in the lab test runs.

test/util/xml_utils_unit.js

@@ -425,10 +425,15 @@ describe('XmlUtils', () => {
     });
 
     it('returns null on XML that embeds SVG', () => {
+      // Some platforms, such as Xbox One, don't recognize elements as SVG
+      // based on namespace alone.  So the SVG element below needs to be a real
+      // SVG element.
       const xmlString = [
         '<?xml version="1.0"?>',
         '<Root>',
-        '  <Child xmlns="http://www.w3.org/2000/svg"></Child>',
+        '  <svg viewBox="0 0 100 100">',
+        '    <rect x="0" y="0" width="100" height"100" />',
+        '  </svg>',
         '</Root>',
       ].join('\n');
       const doc = XmlUtils.parseXmlString(xmlString, 'Root');