refactor: Improve $http_response_header forward compatibilty to avoid false positives

See php/php-src#19611, keeping the deprecated variable name leads to false positives

Author: DannyvdSluijs

src/JsonSchema/Uri/Retrievers/FileGetContents.php

@@ -51,17 +51,12 @@ 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.
-            $this->fetchContentType($http_response_header); // @codeCoverageIgnore
-        } else {                                            // @codeCoverageIgnore
-            // Could be a "file://" url or something else - fake up the response
+
+        $httpResponseHeaders = PHP_VERSION >= 80400 ? http_get_last_response_headers() : $http_response_header ?? [];
+
+        if (!empty($httpResponseHeaders)) {
+            $this->fetchContentType($httpResponseHeaders);
+        } else {
             $this->contentType = null;
         }
 
@@ -73,7 +68,7 @@ public function retrieve($uri)
      *
      * @return bool Whether the Content-Type header was found or not
      */
-    private function fetchContentType(array $headers)
+    private function fetchContentType(array $headers): bool
     {
         foreach (array_reverse($headers) as $header) {
             if ($this->contentType = self::getContentTypeMatchInHeader($header)) {