Merge branch '4.4'

* 4.4:
  fix PHP 5.6 compatibility
  [Cache] fixed TagAwareAdapter returning invalid cache
  Add plus character `+` to legal mime subtype
  Make Symfony\Contracts\Service\Test\ServiceLocatorTest abstract
  bug #33942 [DI] Add extra type check to php dumper
  [Dotenv] search variable values in ENV first then env file
  [PropertyInfo] Respect property name case when guessing from public method name
  [VarDumper] fix resetting the "bold" state in CliDumper
  Missing argument in method_exists
  SCA: added missing break in a loop

Author: xabbuh

HttpClientTrait.php

@@ -199,7 +199,7 @@ private static function normalizeHeaders(array $headers): array
         $normalizedHeaders = [];
 
         foreach ($headers as $name => $values) {
-            if (\is_object($values) && method_exists('__toString')) {
+            if (\is_object($values) && method_exists($values, '__toString')) {
                 $values = (string) $values;
             }