use strcasecmp() as fallback ensure different combination of case

Author: samsonasik

src/Middleware/Mezzio.php

@@ -101,7 +101,7 @@ private function showDefaultView(): Response|HtmlResponse
         /** @var  ServerRequestInterface $request */
         $request          = $this->request;
         $isXmlHttpRequest = $request->hasHeader('X-Requested-With')
-            && $request->getHeaderLine('X-Requested-With') === 'XMLHttpRequest';
+            && strcasecmp($request->getHeaderLine('X-Requested-With'), 'XMLHttpRequest') === 0;
 
         if (
             $isXmlHttpRequest &&