Merge branch '4.4' into 5.1

* 4.4:
  [HttpFoundation] Drop int return type from parseFilesize()
  Added $translator->addLoader()
  bug symfony/symfony#39878 [doctrine-bridge] Add username to UserNameNotFoundException
  fix spelling
  Add check for constant in Curl client
  Revert #38614, add assert to avoid regression
  Fix problem when SYMFONY_PHPUNIT_VERSION is empty string value
  Update PHP CS Fixer config to v2.18

Author: derrabus

CurlHttpClient.php

@@ -170,7 +170,7 @@ public function request(string $method, string $url, array $options = []): Respo
             $curlopts[\CURLOPT_DNS_USE_GLOBAL_CACHE] = false;
         }
 
-        if (\defined('CURLOPT_HEADEROPT')) {
+        if (\defined('CURLOPT_HEADEROPT') && \defined('CURLHEADER_SEPARATE')) {
             $curlopts[\CURLOPT_HEADEROPT] = \CURLHEADER_SEPARATE;
         }