Fix reporting of risky tests

Signed-off-by: Arthur Schiwon <blizzz@arthur-schiwon.de>

tests/lib/TestCase.php

@@ -184,7 +184,9 @@ protected function tearDown() {
 		// fail hard if xml errors have not been cleaned up
 		$errors = libxml_get_errors();
 		libxml_clear_errors();
-		$this->assertEquals([], $errors);
+		if (!empty($errors)) {
+			self::assertEquals([], $errors, "There have been xml parsing errors");
+		}
 
 		\OC\Files\Cache\Storage::getGlobalCache()->clearCache();