tests: Fix codesniffer issues

Author: tvdijen

tests/SAML2/XML/md/ExtensionsTest.php

@@ -60,7 +60,7 @@ public function testExtensionAddEmpty(): void
     <ns:SomeChunk xmlns:ns="urn:some:ns" foo="bar">Contents</ns:SomeChunk>
   </md:Extensions>
 </root>
-XML
+XML;
         $this->assertEquals(
             $xml,
             trim($d->saveXML())
@@ -142,7 +142,7 @@ public function testAddExtensions(): void
     <alg:DigestMethod xmlns:alg="urn:oasis:names:tc:SAML:metadata:algsupport" Algorithm="SomeAlgorithm"/>
   </md:Extensions>
 </root>
-XML
+XML;
         $this->assertEquals(
             $xml,
             trim($r->ownerDocument->saveXML())