Merge branch '6.4' into 7.0

* 6.4:
  [Mime] Fix lowest versions of deps
  [VarDumper] Fix calling scope detection inside magic accessors
  [Validator] add missing German translations
  fix deprecation versions
  update the Brevo SMTP host
  Remove \ReflectionProperty::setAccessible(true) calls
  [Serializer] Fix denormalizing abstract part headers in MimeMessageNormalizer
  Fix property must not be accessed before initialization on SymfonyRuntime::$input
  [Form] Remove an obsolete phpdoc comment
  [Webhook] Allow slash in webhook type
  Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls
  [FrameworkBundle][Workflow] Throw exception is workflow.xxx.transitions is not an array

Author: nicolas-grekas

SymfonyRuntime.php

@@ -106,7 +106,7 @@ public function __construct(array $options = [])
                 ->usePutenv($options['use_putenv'] ?? false)
                 ->bootEnv($options['project_dir'].'/'.($options['dotenv_path'] ?? '.env'), 'dev', (array) ($options['test_envs'] ?? ['test']), $options['dotenv_overload'] ?? false);
 
-            if ($this->input && ($options['dotenv_overload'] ?? false)) {
+            if (isset($this->input) && ($options['dotenv_overload'] ?? false)) {
                 if ($this->input->getParameterOption(['--env', '-e'], $_SERVER[$envKey], true) !== $_SERVER[$envKey]) {
                     throw new \LogicException(sprintf('Cannot use "--env" or "-e" when the "%s" file defines "%s" and the "dotenv_overload" runtime option is true.', $options['dotenv_path'] ?? '.env', $envKey));
                 }