use call_user_func() for PHP 5.3 compatibility

Not all callables can be called directly on PHP 5.3 (for example,
`array('className', 'methodName')` does not work).

Author: xabbuh

src/Symfony/Bridge/PhpUnit/ErrorAssert.php

@@ -53,7 +53,7 @@ public static function assertErrorsAreTriggered($expectedType, $expectedMessages
                 $triggeredMessages[] = $message;
             });
 
-            $testCode();
+            call_user_func($testCode);
         } catch (\Exception $e) {
         } catch (\Throwable $e) {
         }