Fix PHP 8.5 $http_response_header deprecation on 5.x.x (#857)

As requested in
#841 (comment)

Author: gnutix

src/JsonSchema/Uri/Retrievers/FileGetContents.php

@@ -49,6 +49,11 @@ public function retrieve($uri)
         }
 
         $this->messageBody = $response;
+        if (function_exists('http_get_last_response_headers')) {
+            // Use http_get_last_response_headers() for BC compatibility with PHP 8.5+
+            // where $http_response_header is deprecated.
+            $http_response_header = http_get_last_response_headers();
+        }
         if (!empty($http_response_header)) {
             // $http_response_header cannot be tested, because it's defined in the method's local scope
             // See http://php.net/manual/en/reserved.variables.httpresponseheader.php for more info.